i bought 2 used xp4's in perfect running condition, both for under $120 each. check craigslist, ebay and the classifieds here. good luck! xp filters are great and cheap, lots of reviews here.
Dollar for dollar, there isn't a better filter available. I have two and both are whisper quiet. It's been awhile since I bought one, but I think they're in the $75 range new. You would have a quality filter that will give you years of service...and plenty of cash leftover to buy other supplies.
As another member mentioned, you could go used and with $120 available, your choices are nearly infinite. If you really have to stay with a canister (don't get me wrong, I am a HUGE fan of canisters), I would definitely go used and get a high quality, name brand filter versus a new, inferior unit. Fluval, Eheim and Rena all have a large fan base.