Texsport makes cheap dry bags and a few other things that I've seen at walmart. I would have never guessed they made rafts. I always thought the raft pictured were real old Riken rafts.
While it does look like it is in good shape I'm going to guess it is around 20 years old. Make sure it can actually get firm when inflated (some of the old boats suffer from ED) the material may be stretched out. Look for old rotted glue, leaks at the seams and valves and blown baffles between the chambers (meaning you don't need to use all valves to inflate the boat and it may sink if you pop it).
If all that is good I still wouldn't pay more then $200 for it (more like $50). With all the new cheap rafts from China for around $1500, old, used bucket boats aren't worth much anymore. I'd probably take $200 for my 20 year old self-bailer (you fix the floor, good luck).