I have a 1992 TVR V8S, hence the username. They're pretty rare now, with anywhere between 50 and 150 still on the road.
Had it since 2004.
I've been around TVR since I was a kid, thanks to my elder brother owning a 3000M and then a 350i. Now, my elder brother, middle brother (400SE) and I own TVRs.
Don't listen to people who tell you they're unreliable. They're built from bits from other cars that have been tested. Ford indicators, Vauxhall light assemblies, Range Rover switch gear etc.
It's mainly the bad TVR wiring that causes issues, and rust on chassis outriggers. The Rover V8 is pretty bullet proof and, because everything is fairly simple, servicing can be done yourself with a bit of effort.
I can't speak for Tuscan and later models. They had a lot more TVR-specific bits. Cerberas especially seem to suffer electrically.
The new TVR company owners have recently been buying up lots of parts companies and stock, to have a central parts store so hopefully availability will improve. There are some parts that are almost impossible to get though, like the window toggle switch for the S series (Triumph part I think) and the front indicator lamps (off a Leyland van).
Since 2004, I've really had very few problems with my car, and it's now 24 years old so you can expect a few things wearing out.
Throttle cables tend to wear out on the S series where they go through the bulkhead, the stepper motor that controls idle on the V8 is a pain (though many people have no problem but it does eventually fail and it's £100), I've had a fuel pump and fuel pump relay go and a connector burn out by the ignition. I can't think of anything else particularly. I've done about 30,000 miles in it in all weathers including snow. It's not a garage queen and has led convoys of sports and supercars through tunnels and Welsh valleys.
Main cost is LOTS and LOTS of fuel. That said, I do drive it hard. On a motorway run in 5th at a steady pace, you're looking at around 25 mpg. The engine is uber-smooth and lightly stressed so always has performance.
It's really cost me more in non-essential maintenance than fixing things, like four point harness, GAZ Golds, good tyres, wheel refurbishment, trying to get the damn doors to fit properly...