A bit like you I wanted a bike but wasn't sure how much I would use it so didn't want to spend a lot, so I bought this Cove Stiffee FR off facebook marketplace about a week ago.
It had been left in a shed for 5 years so I used it as an opportunity to learn a bit about bikes, I stripped it down to every nut/bolt, degreased and cleaned everything, completely rebuilt the Hope brakes and bled them and just learnt from videos on YT on what to do, a few new seals and cables and I'm in it for about £350.
I took it on a mtb track yesterday with my son and it was great fun, even better that I put so much effort into restoring a nice hardtail. I made sure the forks had the correct air pressure for my weight but next job is a fork rebuild, some good bargains out there if you troll the private ads, just make sure its not nicked!