I bought a bunch of slimline DVD+/-R drives on ebay a while back for $10 apiece that were working pulls from laptops. They're not slotloads, but I seem to recall seeing some listed that were fairly cheap. I bought mini-SATA cables on ebay for a couple bucks apiece and a bracket that accommodates both the slimline drive and an SSD from Newegg for about $7.99. I also bought some external cases with faceplates and USB cables for the drives for about $7 each.
If you're talking Blu-Rays then that's an entirely different ballgame. A slimline slotload BD-ROM isn't going to be cheap. You might be better off getting a full-sized drive and putting it in an external enclosure so you can connect it when you need it. If your case and mobo support eSATA then that would give you the best transfer rates between the drive and the PC. USB is fine but will be painfully slow for ripping Blu-Rays.
If you're talking Blu-Rays then that's an entirely different ballgame. A slimline slotload BD-ROM isn't going to be cheap. You might be better off getting a full-sized drive and putting it in an external enclosure so you can connect it when you need it. If your case and mobo support eSATA then that would give you the best transfer rates between the drive and the PC. USB is fine but will be painfully slow for ripping Blu-Rays.