My site has this to say:
"Now, which car to start with (see)? Heres your choices:
Chrysler PT Cruiser (145hp/1270kg) 17980cr
VW Beetle (109hp/1256kg) 15930cr
Daihatsu Cuore (61hp/700kg) 11140cr
Daihatsu Sirion (114hp/840kg) 13900cr
Mazda Demio (95hp/960kg) 14660cr
Mazda MX-5 89 1.8 (130hp/980kg) 16900cr
Mazda MX-5 89 1.6 (114hp/940kg) 17000cr
Suzuki Alto (61hp/710kg) 12220cr
Toyota Trueno (?hp/925kg) 13550cr
Toyota Yaris 1.3 (?hp/?kg) 12880cr
Toyota Yaris 1.5RS (?hp/940kg) 14530cr
The Cruiser is extremely ugly, very expensive (no room for modifications here) and lurches around a bit.
The Beetle has a very low Power-to-Weight ratio and is phenomenally ugly. At least it opens the Beetle Cup to you though. For you to lose badly.
Amazingly the Cuore TR-XX-XX-XX-XX-4R-RT-TX-XR-X4-TX-XT-RX-X4-4R has an even lower PWR. Its 4WD, so can lose in those races and has bugger-all potential, save for Kei Cup races. Its cheap though.
The stablemate Sirion has the highest PWR of the lot here, but it rolls around a lot and isnt very pretty at all.
The Demio is a Demio. Havent you been paying attention?
The MX-5s open the most competitions for you (NA tune for NA cup, Turbo tune for Turbo cup. They even have their own Endurance race for totally unmodified MX-5s), have a high PWR and are quite attractive.
The Alto is a Cuore, but worse and more expensive (go figure)...
The Trueno is more powerful than the MX-5s (and FR too) and cheaper.
The Yaris 1.3 isnt much good, but the 1.5RS is the best small FF, and has its own competition (although you may want to tune the thing first)."
So for your 18,000cr, the car which will sell back for the most is the Chrysler Cruiser (what a heap of...).