iRacing is where it's at. It's multiplayer only though... and much like real life, you're in a set class, and you race and practice one car per class. Of course you can run more than one, but that makes it hard on you 'cause you can't really get to know your chosen car properly. Races are sanctioned once per hour, with open practice sessions in between. Races in C class and higher are once every 2+ hours 'cause there's more emphasis on practice... as the races are more important.
There's also a safety rating sysem in place to stop people driving like asses without consequence.
The initial monthly subscription fees grant you access to all cars and tracks needed for your Rookie season, then from D-class upwards you need to buy your cars and tracks. It can get pricey if you try and run more than one car. Also, tracks change once per week, so you don't need to lash out lots of money straight up front. It's not too bad if you think about it logically.
If you're not interested 'cause of the costs, you're going to have to wait for GTR 3 and/or rFactor 2.
On the off chance you do get into iRacing, post your profile on here and I'll add you to my friends list.
I'm C-class, but racing the MX-5 series (Rookie) 'cause I love the car.
Also, my personal car suggestions for the first three classes;
Rookie - Mazda MX-5 Roadster
D-Class - Ford Mustang
C-Class - Star Mazda
(...and Hello Commander!)