Well I don't really regret this but I was a dumb ass to buy it so here is the story anyway.
I bought a turbocharged 05 350z with like 5k miles. The car was a show car before I bought it but I had a nissan mechanic look at it before the purchase. He said mechanically its good to go but had some electrical problems. At one point it had lambo doors on it. Well they decided to change it back to regular doors before they sold it. So after the test drive I pretty much didn't care about the electrical stuff. The thing was fun and quick as hell, kept a ear to ear grin on my face the whole time. I had to have it.
So after purchasing I decided to go get the electrical shit done. I found out that when they took the doors off they just cut all the wiring and half ass spliced to together... Took a dude like 4 hours to sort it out and fix everything. It also had a nitrous express kit mocked up in it. It wasn't 100% hooked up but probably 95% and I knew that but the way they did it was a pain in the ass to remove. It also had a sound system that wasn't properly wired and they also didn't bolt the sub box down in the back so it would just fly around from time to time.
So basically a month after buying it I spent $2000 to get all the wiring fixed and all the other shit done. I sold the NX kit for like $300 so I recovered a little bit.
6 months later I have an issue with something in the turbo pluming. Some bolt fell out and thank god my neighbor had a lift and I got it up there to find the little bolt with carbon on it stuck between some sit. I found the hole where it came loose about 5 mins later. If I didn't find that it would have taken forever to diagnose and fix the problem. So that cost like $3 for a new bolt and like 1 hour to try to put that fucker in, everything was so tight and getting a wrench on it was extremely difficult.
3 months later the middle of summer in AZ hits I am driving my car and all the sudden white smoke is coming from the engine compartment. Fuck.... so I think wtf the car still was driving great didn't feel any issues but then the ac was out. Luckily I was 10 mins away from my shop so I took it over. The turbo melted the ac line... Boom $600 for a custom line. I guess it is a common problem with the turbonetics kit on that car.
When I picked it up I was planning on hanging out with a friend of mine. So when entering his neighborhood I hit a bump and all the sudden I lost all power. No steering, engine shut off etc. Well my mechanic forgot to tighten one of the turbo pipe brackets and a pipe came loose... Luckily no damage happened and I just put it back in place and tightened the bracket and was good to go.
So time to get my car passed through emissions, well it didn't have a cat so I had to get a cat and get it put in place. For the straight pipe cut out and the cat it cost like $600. Passed emissions and swapped the cat out for the straight pipe.
I had someone trying to steal my cool carbon fiber low profile antenna, they broke it(only like $40) and it also broke the internal antenna so that was like $400 to replace and fix.
There was some other little shit that I can't remember.
No real problems for about a year and I sold it.
But all in all it cost about $4000 extra to own over the 2 1/2 years I owned it. I don't really regret it because the thing was an absolute blast to drive. It was pretty stupid of me to buy it without having it more thoroughly checked out, the test drive foolishly had me sold. I couldn't make an intelligent decision after driving it, I just had to have it. Pretty dumb move but it all worked out and it was an awesome car to drive. I did learn an important lesson from that and it is to not get overly excited when buying something and to make smart decisions when buying shit.