Well if she doesn't like the C5 vert, what about a late-model C4 vert? That should be about in your price range, offer an absolute plethora of aftermarket parts, and not be "too big or clunky" for you fiance'. It sounds to me like she is stuck on the girly roadster type of car, so I guess that might not be an option then. I'd seriously look at the Sky and new Miata. Keep in mind, the MX-5 is better out of the box, but you can put any LS-based small block Chevy in the Sky.
LS6 in Solstice 
