You can usually pick up a Canon 814 Auto Zoom on ebay for $80-120. That's the route I would go. They have good optics, are built like tanks and even when they aren't working right, still work. LOL. If you get into the more expensive 814 XL-S and 1014 XL-S cameras, they are possibly the best Super 8 cameras but when the stop working or have an issue, they just stop functioning.
There are lots of other good options for the $100 range. You'll see some Nizzos go for that.
Stay away from any of the cheap Kodak cameras from the 70s. They have terrible optics and generally can only read Type A (40 ASA) or Type G (160 ASA) film, neither of which is made anymore.
Super 8 Data has the best specs on Canons:
If you are doing negative film with telecine/scan transfers, remember that you will want:
1.) Something that can auto expose at least up to 250 AND down to 40.
2.) Something that can shoot at 24 FPS
3.) Stay away from the 300 and 500 series canons... they are just not up-to-snuff
4.) Beaulieus are probably the best cameras, but can be a hassle to work with if you are not already good with photography/cinematography.
Lots of other opinions are already posted on these forums. Read through.