I just picked up a Vista Carrera 7 from craigslist. Long story short I paid 5$ for it.
The frame seems pretty decent, the components are a mix of okay and crap. The derailluers are suntour and decent, as is the freewheel and sprockets. The wheels are ok. The handlebars are okay.

I broke it down, wire wheeled anything without paint on it, degreased the whole thing, greased all bearings, and now I'm putting it back together.

I only needed to buy tubes, tires, cables and bar tape which is going to cost me 81$ total, so I should have a serviceable bike for 86$. This is where it's at now, I'm still waiting on stuff in the mail.