I've been doing a rolling resto on my Z for the last 2 seasons.
I bought the car with 54,000 miles on it and now it's sitting at 62,000 miles. Only an "occasional" fairweather driver, but mostly long road trips all across the province. I don't hesitate to drive my car distances because i've had it all apart myself and I am particular about noises/vibrations and such.
Anyway, i've rebuilt all my suspension/brakes/u-joints/seals/all bushings and quite a few little odds and ends/cosmetic upgrades.
I've managed to do all of this on less than $12,000 so far includng buying one of the cleanest Z's with the upgrades I wanted (Webers/R200 diff/ZX 5spd/Wheels etc.) so initial buy in was a little more.
We tend to pay more for Z's up here in Canada because they're harder to find that haven't already rusted into a pile. We also generally pay more for parts because everything has to come from the states. So doing all the work myself I figure i'll have between $20 to $25K into it by the time i'm totally happy with it.
The paint isn't perfect but I like to drive it (thought it cleans up nice). I have taken it to track days and killed a set of tires, if I want to look at a perfectly pretty black S30 i've got a really nice scale model in my living room.