I have found that 7 and 8 fastbacks are gone, only a 2008 type recession will bring them back on the market.
7 and 8's bring 30 to 50% more than a 5 and 6, same condition.
Sportyworty is dead right, honest ones are gone from the ads for about 5 years now. The good ones are privately traded.
2 years ago I called on a yellow v8 for10K, and the rust was horrendous. The seller said the buyer just left with it. I asked him if he didn't mind telling me how long it was in CL. He said he put the ad in and 10 minutes later the guy was there and 45 minutes later is when I called. There are some resto mod and non original ones which are going for 45 to 70.
I might suggest using a tape measure to check for hits especially the shock towers and rear quarters, they can be worse than rust. Barring that, here is LA the car will bring 25,28 all day long.