If you're just getting into it, probably go with something that doesn't hold super high value. Brands like Nikon, Olympus OM, Contax, all tend to be really expensive for use as film SLR's, and their lenses tend to be expensive. Nikon cameras and lenses especially tend to be heavily sought after, so they're going to go for a premium.
Go for something like Canon, Minolta, Yashica, and any screwmount SLR from the 60's.
Here's a few you should keep your eye out for.
Minolta SR series. Anything from the SRT 101 of 1966 to the SRT 303b of the late 70's carry very little difference between model (the only big differences tend to be things like mirror lockup, or viewfinders that tell you what aperture you're at). They will all fetch a really affordable price, and the lenses, though actually remarkably sharp and well made (Minolta had experience working with Leitz, and used a lot of that knowledge in their optics) tend to go for scrapmetal prices.
Canon Manual cameras. You can pretty much pick and choose between any, but things like the F1 and the A1 tend to go for a bit more.. around 50+ for the body alone. Cameras like the T90 are basically just Manual Focus versions of more modern cameras, but are very well made and will cost you around 100 for a good one. Those like the AE-1 tend to be the most often found, and will cost 30-40$. If you don't mind having full program, something like the T50 is actually pretty cool, and really accurate. I got one for 3$ and have put quite a bit of film through it. You can pick up something nicer like an FTb for less than 20$ with a lens, though, so keep your eye out. The lenses are okay. Not outstanding, but pretty good. They go for affordable prices as well.
Yashica cameras tend to be really affordable, and have great glass offerings. The FX3 was super popular, but because in modern days nobody knows what Yashica is, they tend to think they're scrap cameras, since they're plasticy and such. But they're actually really decent and give you the ability to invest in Japanese made Zeiss glass later on. I really like the FX-3 super 2000. Great all manual body.
Pentax screwmount and kmount bodies like the Zenit, Ricoh, Cosina and Chinon cameras, and the Mamiya Sekor 1000 tend to also go for cheap prices. Sometimes you'll find cameras branded "Sears" which is pretty funny. They aren't bad. Pentax screwmount lenses don't tend to cost a whole lot, and are pretty decent. Pentax K mount bodies like the K1000 tend to go for a bit more, but those like the ME and MV1 go for really cheap - they are aperture priority only.
Just go to your local goodwill and see what they have.
Have a nice day, Bluename.