The Skill Shop is located on the Progress tab of the main menu.
There are three pages of skills - Festival Boss, Skills, and Instant - and each of them have a car as the reward for making it to the top of the tree. Taking the path up the middle is the most efficient and will cost you as follows:
Festival Boss - Bentley Continental GT (36 Points)
Skills - Lamborghini Gallardo LP 570-4 Superleggera (46 Points)
Instant - '65 Mini Cooper S (21 Points)
Thanks to
iTz Canada Ehh for corrections cause I'm an idiot