WARNING! THESE ARE PAY MODS!
But if you like Formula cars, they do a bloody good job.http://racesimstudio.com/
I've got the F2, F4 and Formula79 and they're all excellent.
I haven't bothered with the Formula Hybrid as I feel I have enough modern F1 cars through various other mods and AC itself.
It's pay what you want but the minimum is 3.99 euro, or a little over $6.
This just about completes my full-house of formula cars, except the very rare Formula 5000.....