Hey man. Definitely check Craigslist. Around my area (Appleton, WI) there's PSP 2000s that sell for $60. All Phat PSP are hackable. If you are buying a Slim, make sure to ask for the serial number though. (This would be on the bottom of the PSP or behind the battery, same number basically)
TIP: If it's Piano Black, and the serial number starts with HU00, BUY IT no matter the condition. It's got a TA-085v1 motherboard, I got two of them this way
And I recommend Slim PSPs. IMO Phats are too heavy to carry around. Slims have more memory capacity too.
As for mods, on my first Slim I have an internal CR-3100 (Google it, but I wouldn't recommend this anymore). My second Slim is stock yet (with a CR-5400), but when I find time I'm going to be adding backlit buttons*, jewel, chrome faceplate (silver backing), and a custom tribal tattoo design spray painted over the front and back with transparent green spraypaint (as to keep the chrome effect).
*Yes. Backlit.
Like my keyboard ~Ennon