Man it's been a looong time since I joined up but I'm pretty sure you at least get the new Global MX-5, the last gen NASCAR truck and IndyCar. Tracks I believe Summit Point, Laguna Seca, LRP for road and Charlotte, Daytona (2008 version) and Phoenix (older version, not sure of year) for ovals. May be more though by now.
No free GT3 cars unfortunately, as you can't drive them initially with only your rookie license. As long as you're a safe driver you can progress up to higher licenses surprisingly quick, like a week or two to land your D or C license. Safe driving is KEY in iRacing, especially just starting out. I really can't stress this enough. Most people who give up on it, in my experience, leave because they can't seem to get out of Rookies. I always see complaints on the forums about getting wrecked out of every race from frustrated rookies. I would recommend not even worrying about actually racing anyone for position when you first start; just drive safe, avoid all the inevitable wrecks, and get your D license before you judge whether or not iRacing is worth your time and money. The rookie license is more of a safe drivers 'test' and race results don't count until you get your D license anyway.
The cars and tracks can seem expensive, roughly 10-15 bucks each, but they are VERY well made and the tracks are all 100% laser scanned. Not at all like cars in huge 20+ car DLC packs for games like Gran Turismo and the like. You also don't need to buy too many to compete in a full season as there are normally schedules posted telling you which tracks will give most bang for buck in the upcoming season.
We are presently in season 2, week 7 of 12 and there are 4 seasons per year.
edit - Sorry for the wall of text when all you asked about was car prices, lol... I was pretty much just writing out what I would tell myself when I first started out in rookies if I was able.