Nismos start at £18,000. Tbh the production has pretty much ended for it so prices are stagnated.
What was overpriced 6 months ago is now asking price. If anyone thinks 20k is overpriced for a mk 2 Nismo then best of luck finding a clean one for less.
Nothing wrong with an older Z, just check the regular things, steering lock, gallery gaskets and slave cylinders/clutchs. Other than that nothing I can think of.
You can probably get a clean 2013-2015 GT model for around 13-16k at the lower price.
Crazy thing I saw a 2015 convertible a few months back not sure if it was sold. Very rare I reckon it got imported or sat around for a few years before being sold to the first owner.
Try find one with good history and receipts. Or like Ollie suggested wait a little longer and get a post 2013 but will be at least another 5k on top. Summer time car prices will be up though