This is great story on Jalopnik about a guy who prepared a 1991 BMW to run in the FIA-sanctioned Rally Mexico, and he finished 3rd in class. How A $500 Craigslist Car Beat $400K Rally Racers - Rallying - Jalopnik
Here's part 2 - the co-driver's perspective. Even after this, there is much story left to tell! I Co-Drove The $500 Craigslist Rally Car - Rallying - Jalopnik