I agree with the above post regarding your price range. I looked in the $1000 range for about a year and a half, constantly checking the buzz and my regional classifieds. What I found is that there isn't much middle ground for used rafts. Owners usually buy a new one and run it until it doesn't float any more. I found a lot of 20+ year old rafts for several hundred dollars and most of them couldn't guarantee to hold air more than a day. The next step up was a really nice used raft in the $2k+ range and at this point you might as well buy new.
I thought I found my boat when I bought a used Riken raft for $350 that "holds air well." That it did until I discovered it had a blown baffle between it's only 2 chambers just 3 days before a planned trip. Too risky for me. Ended up calling a local guy who imports PVC boats from China (think Saturn) and he had 2 left in the size I was looking for. Paid $1400 for a brand new boat and I love it. Hardcore gearheads and boat snobs will grill me for this (haters gonna hate) but I feel like I made the best decision for myself. Took it on the San Juan a few weeks ago and loved it. Also should note I am a more casual boater (2-3 trips a year).
So FWIW I would recommend upping the amount your willing to pay or going with something like myself. It's just not worth getting a used boat in that range that may have a lot of problems.
If you're interested here is the guy that sold me my boat (in SLC, UT):
Classifieds for Utah, Idaho, and Wyoming | ksl.com
Your Site Name - Boats - Boats
He had one 14' left as of a few weeks ago, but I think he can always order more and can even get them made custom(not sure the price difference). I'm convinced these are made in the exact same factory as the Saturns or any other chinese PVC boat you can find online). If not, they are extremely similar.