I want to make a pristine vocal track, in particular, sound sorta lo-fi. Maybe even lo-fi and gritty. And I may want to make the whole project sound that way as well, don't know yet. 
I would imagine re-amping the track(s) thru a guitar amp would do it; each different amp/speaker would give you tons of options. 
Are there free (or inexpensive) plugins that would do the trick?   Other ways to do this ?
On Brooks and Dunn's "Boot Scootin' Boogie", it seems to me they did this somewhat to the vocal track on that song... maybe the whole song... not dramatic, but seems it's there. 

Just saw this yesterday.
 
https://www.gearslutz.com/board/new-product-alert/1029819-studiolinkedvst-record-player-fx-plugin-aax-au-vst.html
 
Maybe there is a 78 preset in there.

Depends on how you define "lo-fi." Like the distortion on industrial vocals? The sound of a singer shouting at a mic on the ceiling, like the original "Louie Louie"? Ambience that makes it sound like it was recorded somewhere strange? There are plenty of tools in SONAR which, if abused, can create very lo-fi sounds.
 
If you want more of a vintage vocal sound, try the Classic CA-X amp (in the Clean folder) with the drive turned down. The Jazz amp might also be a good choice.
 
For something more extreme, some of the processors in the Anderton Collection can be converted into Agents of Destruction without too much effort - Try Drum Loop mangler for angry aliens, or Hardcore Drums. The VoxTools FX chain has a Mayhem module that's sort of early NIN-ish. 
 
 

Just mess around with a dedicated bus you send everything to for the desired time range using things like EQ, tape sims, exaggerated compression settings, tube and tape saturation and things that introduce "noise".
 
Put it in the FX Bin of the bus and automate it all for that momentary effect (you could do this a send automation so everything goes to that bus for the desire time while the main track is silenced).
 
If you look at the Blue Tubes suite there is an effect that has year based settings that works well for throwback stuff. The old Cakewalk Tape Sim has a "Noise" feature that introduces some scratchiness. A lot of EQ's will have a "telephone" preset that yanks out a ton of lows and makes things sound very lofi (and you can create this effect manually if you google Telephone Effect EQ).
 
There are of course third party plugs that can do this instantly but yanno... you might have to pay and since it's not that hard to do with what is already included in Sonar so it's just a matter of how much it's worth to you to get this effect versus learnign to create it on your own.
 
Ideally though I'd imagine you'd want some kind of Vinyl Emulator effect if you were going third party.
 
Just some thoughts.
 
CHeers.
 
Edit: Just remembered the Blue Tubes plug... It's the Oilcan Reverb and it actually does a pretty good job at just automatically creating a vintage lofi sound BUT I would personally do some other stuff to really nail the effect. Check it out. It might get you most of the way where you want to go.

This is a nice free tool for going LoFi:
 
https://www.izotope.com/support/download/vinyl
 
 
 

Anderton
Depends on how you define "lo-fi." Like the distortion on industrial vocals? The sound of a singer shouting at a mic on the ceiling, like the original "Louie Louie"? Ambience that makes it sound like it was recorded somewhere strange? There are plenty of tools in SONAR which, if abused, can create very lo-fi sounds.
 
If you want more of a vintage vocal sound, try the Classic CA-X amp (in the Clean folder) with the drive turned down. The Jazz amp might also be a good choice.
 
For something more extreme, some of the processors in the Anderton Collection can be converted into Agents of Destruction without too much effort - Try Drum Loop mangler for angry aliens, or Hardcore Drums. The VoxTools FX chain has a Mayhem module that's sort of early NIN-ish. 

If you check out Boot Scootin Boogie, you can hear what I'm referring to...  the vocal is not pristine, and maybe even  just a tad gritty and in your face. Seems like the lows are cut. Not studio 20-20Khz stuff. it's a bit of distortion there for sure, don't know what kind, but it kinda gives it that vibe of being recorded from a PA system or live or something, not in a studio with 20-20K response. 
I know I can come up with this somehow re-amping the tracks, if that gives you a better idea of what I mean, but that could be a long involved and not always rewarding or reproducible pursuit.  Plug-in(s) would be great. 

SF_Green
This is a nice free tool for going LoFi:
 https://www.izotope.com/support/download/vinyl
 

You can download this, but it's discontinued, and will only operate in trial mode, whatever that means...

Beepster
Just mess around with a dedicated bus you send everything to for the desired time range using things like EQ, tape sims, exaggerated compression settings, tube and tape saturation and things that introduce "noise".
 
Put it in the FX Bin of the bus and automate it all for that momentary effect (you could do this a send automation so everything goes to that bus for the desire time while the main track is silenced).
 
If you look at the Blue Tubes suite there is an effect that has year based settings that works well for throwback stuff. The old Cakewalk Tape Sim has a "Noise" feature that introduces some scratchiness. A lot of EQ's will have a "telephone" preset that yanks out a ton of lows and makes things sound very lofi (and you can create this effect manually if you google Telephone Effect EQ).
 
There are of course third party plugs that can do this instantly but yanno... you might have to pay and since it's not that hard to do with what is already included in Sonar so it's just a matter of how much it's worth to you to get this effect versus learnign to create it on your own.
 
Ideally though I'd imagine you'd want some kind of Vinyl Emulator effect if you were going third party.
 Just some thoughts.
 CHeers.
 Edit: Just remembered the Blue Tubes plug... It's the Oilcan Reverb and it actually does a pretty good job at just automatically creating a vintage lofi sound BUT I would personally do some other stuff to really nail the effect. Check it out. It might get you most of the way where you want to go.

Will try all these things unless there's a simple cheap or free plug-in that'll do the trick... 

Honestly you may be better off doing the extra work to add those elements individually to tracks and/or sub-busses instead of all on a final output bus (even with a plugin). That way you can control how vintage everything sounds and tweak it all just right for maximum effect. That's a lot of work though.
 
I'm kind of thinking how Portishead got that flowing mix of lo and hi-fi on those absolutely amazing sounding tracks. That all seemed to be a mish mash of effects on various elements of the tunes to create that mood/feel and could be exagerated as needed.
 
I've been playing around with full "master" bus stuff like that (but not for lofi technique yet) a bit and really trying to make drastic changes on EVERYTHING at once inevitably makes it sound a little forced and unnatural. So I'm thinking going for a cumulative effect makes sure you can get each element sounding just lo-fi enough without over (or under) doing it on everything else.
 
If that makes any sense...
 
but of course there are plugs that are supposed to just make it happen. I gotta wonder how realistic something like that would be though.
 
Cheers.

Oh and don't forget how much switching to Mono can add to the lo-fi effect.
 
Google "mono-izer" and it should bring up ways to use plugs like Channel Tools to achieve an automated mono effect (there is actually a vid on Groove3 that shows how to do this but you gotta have a membership to see it... basically the guy just automates Cahnnel Tools to temporarily make everything mono but this could also be done with sends and a mono bus or multiple mono busses).