These cars were pretty hot when they first came out, I remember seeing one race a vette(vette won.. vette was sandbagging though). I believe they had a dohc 4.6 and had about 285hp. I don't know about 'hot rodders' buying them for retro projects, wouldn't surprise me. The price figures you quoted seem a deal to me. I'm willing to bet there is a web site out there exclusively for mark viii owners though. The mark vii was nice but the mark viii was a huge improvement in performance. I like a v8 t-bird but I'd have to say a mark viii is 'one upping' the bro just fine. Those cars were very expensive and everyone wanted one.
I just found this site, hope it helps..
http://lsc.netherealm.net/MK8diff.html