Tires will cost you about $1000+. The radio might be similar as they had the Bose (which is never cheap to replace/repair). I believe that 3rd gear thing can be one of a few things:
http://www.zfdoc.com/faq.htm
I'm not the price-watcher, but I'd say that's slightly high. Maybe take $17-18k as the price and subtract the repairs necessary from that?