You can get a used SLK55 AMG for ~$45-50k. It's a V8, 355hp, 376 lb-ft, convertible hardtop. That's a pretty nice machine and tad faster than a new Boxster S. (I'd still pick the S any day of the week, but if you're tired of the pcar for some reason).
See
http://www.mbusa.com/models/features/specs/overview.do?modelCode=SLK55&class=07_SLK