How do I gain many cars ?

Max out the lower class cars and catch people off guard, or take a higher class car that looks like the lower ones and only upgrade the grip on the tires to max, reduce the weight as much as you can, throw on nos, and maybe a couple other small upgrades, doing this will keep your cars rating number low enough to race the noobs and you can probably steal their cars and work your way up if you really want to be a dick. Or you can get an A class car like the supra for example which is only like 85K that makes 100 bucks for each perfect shift and 700 a win whilst you are still reciting the sponsor money for your first 20 wins in a day. Also playing through the campaign will get you 1 car from each class, bet ones being the Honda for D class, scion for c class, subaru for b class, Acura for A class, McLaren for S class, and either the Scion or Mazda for the R class, you do need to upgrade your cars decently well to beat some of the races in campaign but you can also make decent money from it (last race in R class is 100k as well don't forget to do the daily challenges which are really easy if you hit your perfect shifts and give you 760 for each of the 3 races against the same car. Furthermore being part of a clan and participating in the turf wars is a good opportunity to win awesome unique cars, lots of gems and tons of cash if your team ranks in the top 3000 teams :D