Tsukuba with a Civic type R (EK) '97 tuned at 156bhp, 1088kg, 375pp
1,607,750 cash, 158,050 XP includes 170% bonus, with a 200% bonus the cash is over 2mil so it could be a nice little grinder. The car could probably go down another 5-10 pp as I came across the line a couple of seconds ahead
Edit: 150bhp, 370pp good for win, the lead car was a Savanna RX-7 infini III but still came in 1.5 seconds ahead at the line for 1,681,500 cash, 165,300 xp @ 170% bonus
Tune:
All weight reduction (not chassis stiffening)
Engine tune stage 2
Custom transmission
All drivetrain
Custom suspension
-15/-5
12.5/ 8.5
9/3
8/3
6/2
2.0/1.0
-0.20/-0.05
LSD 5/15/5
Ballast 200kg @ 50
BB 7/5
Engine power limiter 76.2%
Gears
1:2.998
2:2.287
3:1.807
4:1.471
5:1.234
6:1.066
F:5.233
2nd Edit: Easy wins at every track and the car could go as low as 350pp for Trial mountain and Toscana as I crossed the line 12 seconds ahead in both races. Just need to adjust the final drive for the other tracks.