So right now I'm deep in the market for a real bass. It's doesn't have to be anything special (I'm a noob), and really I'm hoping I can get away with spending ~$100. I've seen a Greg Bennett Corsair on craigslist recently at that price, and I actually own one GB guitar so it's a deal I wouldn't have minded (had it not been taken down pretty much the next day).
 
What brands are reputable in this case? What should I stay away from?

No brand is safe from having a warped neck. Personally I would be very reluctant to shop in the lower price point without looking at the instrument. Or at least a 100% return free of charge and shipping deal. 
When I try cheap guitars and Basses in music stores the necks are always the issue. 
You can get something used for that price but more like $200 buy's a entry level Bass new. 
I like Fender and Yamaha myself, but there can be many brands you've never even heard of at that price. I picked up a used Hondo for $75 and it's a vintage gem. 

I have been very impressed with Fender's Squier, Vintage Modified series of guitars and basses.  Watch for one that is used if this is still over your budget.

Actually that GB Corsair is still on my local craigslist for $100. Could it be decent? I'd have to say I LOVE my GB Torino electric, so I'm not super-fearful that it's going to be a bad bass since it's at least got the same name on it. I'd bring along some gear to test it out a bit if I do pick it up.
I guess the warped neck issue is definitely something to look out for... about how much damage is that usually done? Like, how difficult is it to then play on a warped neck? (just curious, not that I'd buy one with one)
The Squier has always looked like a nice one, and I love the flat, wide neck of the Squier guitar... if it's anything the same, I'll definitely keep my eyes open for one!

Price isn't the only factor. Cheap can also be great.
 
I had a very nice 1973 P-Bass that everyone loved except me. It looked great and was worth a few bucks, but it didn't sound good. I bought a piece of junk Korean bass for $50 and replaced the pickup for $90. It's still my bass of choice. It sounds and feels great, with a super resonant body. No regrets in dumping the Fender. 

Some of the cheap models by Ibanez are actually pretty decent. Definitely check out Ibanez.
 

I like the 3/4 size Ibanez.  It's more $ but sounds great:
 
http://www.sweetwater.com/store/detail/GSRM20BS
 

Actually, afxr, you bring up a good point.... I AM in the used market, and switching out the pickups (once I get the hang of it, or outsource it) shouldn't be too expensive of a job.
 
Kev, I'll make sure to look at Ibanez. Any particular ones you recommend? I'm not actually sure exactly how much I'll have to partition to the bass, but I know $100 is the MINIMUM. Probably won't be over $125, but I definitely wanna be able to pick it up sometime within the next two weeks before the snow hits.
 
Rimshot, the 3/4 Ibanez looks pretty good.. any trial vids on Youtube? I definitely wanna hear one.
 
I think I'm really looking for something versatile- something that can fit both a smooth-ish, sort of soft, low backing bass, as well as one that can get pretty gnarly in the mids/highs for slap and the Bouncing Souls bass sound. Probably a pickups issue to fix that, I'm guessing

Friend of mine recently picked up one of the less cheap Squier Jazz Basses as a backup because his old US Fender needed a partial refret, fingerboard work and full fret-dress and he needed something to play while the work was done.

Friend actually prefers the Squier, and it has to be said it sounds pretty good.

Bear in mind that the guitar market is very competitive, and corners get cut to keep prices down at the lower priced end of the market. There's usually a much bigger difference between a $200 and $400 instrument than between a $750 and $1500. Which is not to say that good cheap guitars don't exist. They do and if you're lucky you find one. It's just that spending a bit more makes it less likely you'll find a rubbish one.

As for warped necks, they are the exact opposite of fun and can be difficult and expensive to fix (if possible, often a new neck is needed). Same with bad fret jobs, where you get some frets much higher than others, truss rods that don't work, bridges fitted in the wrong place etc.

I would definitely make a point to spend more on a higher quality instrument... sadly I have an approx. set quantity I can spend since the holidays are coming up and I'm a jobless high schooler 
 
I see the warped neck is a big possible issue... I'm gonna make sure to bring some info on quality checks with me, since this will be my first major instrument purchase on my own. 
 
What do you guys think of the Ibanez Gio line? I know they're sort of the 'beginner-bass' and honestly the reviews don't seem to point to something I'm bound to fall in love with. Someone's got a brand new Gio sort of local to me, but I'm still pretty decently content hoping to check out the Samick GB.