While you don't receive prize cars for each race series, you do receive a prize car when you get half the stars and another when you get all of the stars for each class.
I had saved this info from a post I believe I found here but couldn't locate during my cursory search prior to posting this response:
Red Bull X Challenge
Complete Red Bull Kart Masters (Bronze or higher) gives (P) Gran Turismo Red Bull Racing Kart 125 - 10,000 Cr
Complete Red Bull X2014 Junior Masters (Bronze or higher) gives (P) Gran Turismo Red Bull X2014 Junior - 200,000 Cr
Mario Andretti's 1948 Hudson Hot Lap
Complete (Bronze or higher) gives (P) Hudson Mario Andretti's 1948 Hudson - 500,000 Cr temporarily available only - seasonal from 19/12/13 to 17/01/2014
BMW M4 Challenge
Complete (Bronze or higher) gives (P) BMW M4 Coupé - 120,000 Cr temporarily available only - seasonal from 12/12/13 to 12/01/14
Career
Novice (All Stars) gives (P) Renault Sport Clio R.S. '11 - 36,400 Cr
National B (Half of all Stars) gives (P) Lancia DELTA HF Integrale Evoluzione '91 - 54,500 Cr
National B (All Stars) gives (P) Acura NSX '91 - 80,000 Cr
National A (Half of all Stars) gives (P) Dodge Challenger R/T '70 - 75,000 Cr
National A (All Stars) gives (P) RE Amemiya FD3S RX-7 - 100,000 Cr
International B (Half of all Stars) gives (P) Jaguar XKR-S '11 - 175,000 Cr
International B (All Stars) gives (P) Lamborghini Diablo GT2 '98 - 300,000 Cr
International A (Half of all Stars) gives (P) Chevrolet Gordon #24 Drive to End Hunger CHEVROLET SS - 500,000 Cr
International A (All Stars) gives (P) Ferrari Enzo Ferrari '02 - 1,000,000 Cr
Super (Half of all Stars) gives (P) McLaren F1 '94 - 1,000,000 Cr
Super (All Stars) gives (P) Audi Sport quattro S1 Pikes Peak '87 - 1,450,000 Cr
Licenses
National B license gives (P) Gran Turismo Racing Kart Junior - 5,000 Cr
National B license (Gold) gives (P) Alfa Romeo MiTo 1.4 T Sport '09 - 28,500 Cr
National A license gives (P) Honda S2000 '06 - 37,800 Cr
National A license (Gold) gives (P) KTM X-BOW Street '12 - 85,000 Cr
International B license gives (P) Volkswagen Scirocco R '10 - 51,500 Cr
International B license (Gold) gives (P) Mercedes-Benz SL 55 AMG (R230) '02 - 125,000 Cr
International A license gives (P) Land Rover Range Rover Evoque Coupe Dynamic '13 - 60,000 Cr
International A license (Gold) gives (P) High End Performance G37 - 200,000 Cr
Super license gives (P) Tesla Motors Tesla Roadster '08 - 100,000 Cr
Super license (Gold) gives (P) Audi R8 LMS ultra (Audi Sport Team Phoenix) '12 - 400,000 Cr
Missions
National B (Gold) gives (P) Mitsubishi Lancer Evolution VI GSR T.M. EDITION Special Color Pack - 32,980 Cr
National A (Gold) gives (P) BMW Concept 1 Series tii '07 - 70,000 Cr
International B (Gold) gives (P) Lotus Elise Race Car '96 - 137,500 Cr
International A (Gold) gives (P) Ferrari 430 Scuderia '07 - 302,500 Cr
Super (Gold) gives (P) Nissan GT-R N24 GT Academy '12 - 500,000 Cr
Goodwood Festival of Speed
Series 1 (All gold) gives (P) Light Car Company Rocket '07 - 100,000 Cr
Series 2 (All gold) gives (P) Plymouth XNR Ghia Roadster '60 - 1,000,000 Cr
Series 3 (All gold) gives (P) Chevrolet Corvette StingRay Racer Concept '59 - 500,000 Cr
Series 4 (All gold) gives (P) Cizeta V16T '94 - 636,660 Cr
Series 5 (All gold) gives (P) Citroën GT by Citroën Road Car - 1,450,000 Cr
(No prize cars given):
One Make events
B - Prius cup, 86 & BRZ Festival
A - BMW 1 series meeting, Honda Civic Sprint, Mazda Roadster Cup
IB - Lotus Elise Trophy, Chevrolet Corvette Festival
IA - Lamborghini Dance of the Aventador, Ferrari 458 Challenge, Nissan GT-R Masters
S - NONE
Lunar Mission
no prize car
Coffee Breaks
no prize cars
