A start would be N.A.D.A. Official Used Car Guide Company
I would not use it as law, but a guide. I ran a basic test run and came up with $33k as the low retail for the basic 28' slide. If this has the "LS" upgrade pkg, the retail price goes up to $34,500. Add TV, upgraded audio, leather sofa, etc, price goes up. So, yes, the price you mention is good, but I would still try to horse trade a bit.
Alan is right on, winter is a buyer's market. The longer they sit, the more it costs.
I am looking at a 31' Dinette and dealer I was talking with, didn't seem to grasp the fact that he's got a untitled 2006 on his lot and asking darn near retail for it. The 2008s start production in about 4 months, making the 2006 now 2 model years old. Each month that goes by, even though in my case, it's still new, money keeps falling off the table and to the lucky winner of that coach, a BIG hit as the tire leaves the dealership (being that it's soon to be 2 model years behind). I respectfully declined and told him to contact me if he was interested in seriously negoit for it.
Take your time. With gas prices where they are, some of the larger units aren't moving as quickly as say a 23' or smaller. Time and the checkbook are on your side.
Thanks Bob, I'll check on my PMs and do some house cleaning.