I have a great keyboard (Yamaha Motifes8) and a great DAW (Cakewalk naturally) with a cheap audio interface and cheap monitors (all M-Audio). I need to add a cheap subwoofer to get a better, more full sound but I have no clue how to choose one (the helpful online information out there isnt all that helpful). I dont need much at all, but I dont want to short change myself... I've been looking at the $299 Mackie MR10Smk3 10" (120w with 2 TRS ins and outs...perfect), but then for $100 more there is the $399 Turbosound iNSPIRE iP12B 12" (1,000w?? with the TRS ins and outs I need). (does the difference in watts make sense or am I missing something? and will 1000w overpower my monitors and muddy my music)
 
I could really use some good advice on either the above, or better offerings. Also, i'm avoiding passive woofers only because I have no idea how they work LOL...
 
Basically... CHEAP is the name of the game but I'll pay a bit more when the value goes up by a large margin.
 
I appreciate any help you might offer :)

Sub's are a option that you should only use ever once in a while to check a mix. Sure it will make improve your listening experience, but it will alter your ability to make wise decisions about your mixes.  
You would be much further ahead to purchase better monitors that perhaps have accurate low end reproduction.
 
I have a Yamaha Sub I picked up at Goodwill for under $30 and I only turn it on to check for low end artifacts. 
So if you must, I would shop for something second hand as there are plenty of these out there due to the popularity of home theater.  I have bought 3 subs over the last few years and all were under $30 second hand. All are name brands that sold for $100 +

I love these forums LOL, keep the ideas coming... Cactus that makes perfect sense, I'll poke around for a crazy cheap woofer option (though I usually avoid used due to my history with such things) but you opened my eyes to getting better monitors which might do the trick too. I'd likely double my budget for monitors with sound that makes the upgrade worth it...but that's what 0% financing is for.
 
To add some other insight, I do plenty of playing without recording so it would be nice to just have nice full sound (I'm big on strings, orchestra, brass, etc.). I also use the computer for gaming... so I want to hear nastier explosions :)
 
 

Best value for a music monitoring subwoofer (as opposed to a HT sub designed to simulate explosions):
 
Monoprice Studio Subwoofer
 
Includes all the essential features: balanced in/out, variable crossover, phase switch. If you're not in a hurry, it sometimes goes on sale for 10-15% off, or there's the occasional free shipping offer. Good luck!
 
Cheers,
Eddie
 

I got a Polk 12" 300W sub to help me mix... abt $200.  I set my cutoffs on my Yamaha HS8 monitors at 100Hz and the sub to pick up from there.  Pros may laugh at me but I just use commercial reference mixes to get what sounds right to me and mix my stuff appropriately... it can work.  The more W the better usually, and you should be able to turn them up or down to match your system... to a point.  I mean, I'm not going to use my Mackie 18" sub that we use for the band for mixing.  If I had the bucks, I'd get a pro studio mixing sub, but they are usually in the range of $500+.

You might want to skip the sub and spend money on better monitors. It doesnt really make sense to invest in the tools to make great sound if you dont invest equally in reproducing the sound. And a cheap sub is probably the worst investment, unless you're just curious to hear what mud sounds like. I know budgets are a reality but powered monitors (and when you can afford it, it good quality sub) are components that you interact with and rely on all the time. Plus they are long lived and their amortized cost may turn out to be small relative to what you spend on other gear and software.
 
My personal cheap sub story. Years ago I purchased a Samson sub to support better lowend than I was gettjng with 6.5 inch Tannoy passive monitors. The monitors weren't bad but I thought the sub would help because I was using use a lot of bass heavy synths. Set it all up and it was the absolutely worst sounding setup ever. Pure mud in the low end - didnt sound like anything definable just a low rumble that detracted from everything else. Sold everything and bought KRK V8 powered monitors, a huge improvement, but thought they were too present in mid range. Sold them and got JBL 4328 s probably at least 8 years ago. Best investment ever in speakers. Eventually got the 4312 matching sub and it plays beautifully with the matched moniitors. You know it's there but it isn't intrusive unless you want it to be. The sub is a lot of fun to have but by no means a necessity with good monitors.
 
Bottom line is that good monitors are arguably the most important part of your setup. You have a nice keyboard and probably some great vsts. Better monitors will show them off.
 
Brian

I use an Elac Sub.
https://elac.com/product/s10/?r=us
 
It was under $200. I drive it with an second out from my NonPatch into a Behringer MiniMon so that I can control how much input goes into the sub. 
It does not have ins/out for crossover but I'm OK with that. My D5's don't go below 50hz and so I have the Elac set low and just bring it in enough to fill that very low end.
It has an auto power shutoff and is highly rated for such a cheap box. 
It works.

All such great information... geez. 
 
I will be looking into all the directions posed here, all very good arguments. after looking at the subs out there, reading all your input, and considering I can up my budget a bit (I like the comment about "amortized cost" since I would buy where I can get 0% interest for as long as possible), I might just end up getting really nice monitors that handle the low end nicely.
 
I'm not in a huge rush but I'll try to post here with what I actually end up doing just for the heck of it.