I can't really tell. When I first got it, insurance was fairly cheap. But the year after, it went up A LOT. That's before I turbo'd it. Then after I boosted it, insurance was fairly cheap. Then it was off the road and this time it was a nightmare to get cover AT ALL. Adrian Flux wanted £14k. Sky, the original insurers post turbo would no longer insure me. I'm 35 with max NCB.
Currently I'm paying MORE for a 1.5 Renault Clio diesel than I did for my Z the first year. It's also only £100 less than I'm paying for my Z right now all mods declared and like for like.
There's just no consistency in car insurance.
But that said, at 20, do you have the 20k+ you're going to need for the project?