i think u should just win the miata LS by getting all Golds on B lisence ^_^ or you could get the RX-8, Z Concept, Vanquish V12, Viper GTS-R Concept, Impreza Rally Car, or get the Esperante in TT ^_^
and since they're free, you'll be able to use the 18,000 to fix up the new car or just save it for later