Huh? Me and my wife have between us, A 77, a 92TT, and a '04 Enthusiast. The 92TT is the most expensive to maintain, with the 350Z behind it, and the S30 way behind it. That's just maintenance. The only bolt-ons for the 350Z are expensive, and the only ones that are really worth anything are a supercharger kit or turbocharger. And those are real cheap. The Z32 has bolt-ons, but they aren't inexpensive either. Then there's my S30, which has few bolt-ons, but is by far the cheapest to maintain and modify.
I think you meant to say "easy" instead of cheap. Easy if you have money, that is.