Board Thread:Game Discussion/@comment-2A02:C7D:C14:300:E803:F9D:58D6:7E14-20170922160008/@comment-31295789-20170923074303

http://rr3.wikia.com/wiki/RR3_Wiki:Upgrades_Strategy_For_100%25_Completion is the page for you. Tells you which car is cheapest to upgrade for 100% completion on each series. For Classic Ferrari showdown the F40 is the cheapest to upgrade to unlock the Le Mans 4 lapper. -1 Engine (5443333) however you might want to buy the F50 on showcase discount as its showcase event has a good early farming race in it too.