Unless you have a cheap hookup for instant film, i'd pass on the instant camera.. since you have a tight budget. Instant film is pretty expensive these days. I mean, just as an example, 10 shots of polaroid is almost 50 bucks on amazon..
I think for your camera budget, craigslist is going to be your best bet.. that way you don't have to deal with shipping at least. Or local thrift stores.
Also, you didn't mention what kind of 35mm camera you wanted. SLR with interchangeable lenses with lots of controls? That'll cost you more. Point and shoot? You can find useable point and shoots under $20, heck, often under $5 in most thrift stores. They won't be awesome, but they'll take photos.