I just looked it up in bookfinder.com. Whoa. I don't sell books, but I read somewhere to ignore the 3 lowest & highest priced, then go for the middle. Taking condition into consideration. Of course, you never know how much these books actually sold for, but still, all are over $245.
Try looking at ebay, show only completed items. May be more realistic, but the prices are still good. Note that in my experience, ebay is where the best bargains are, so they are priced a bit low? I didn't check ISBN's on ebay so some might not be identical to yours.