The best I got was 1.55.121 in the Supra RZ.
I checked again and the Supra RZ '97 (turbo) was $15,000 but there was also a Supra SZR (NA) for $17,000 so I don't know what's going on there. Just luck I guess.
The 1.55 I posted for the S15 was over the $20k limit, I was in the 56's for that car.
And a tip (even though I'm obviously in no position to give advice!): I found I could take the first, long hairpin faster by running the car against the outside wall. Sounds crazy but I've found it to be a pretty good technique on some rally tracks. Sucks that you can go faster by slamming into walls, not really a "real driving simulator"!
Edit: I got a 154.456 in a GT-R32 N