You most likely have at least 1 Hypercar that was won or given to you at some point in the game, but if you don't the cheapest one available from the store is the 2012 Lamborghini Aventador LP700-4 at 310,000 credits. There are 12 non-DLC Hypercars that are available in the store but as some of them cost over 1,000,000 credits it can get expensive quickly. If you do purchase one of the expensive vehicles make sure to use the Made To Order perk in the Skill Shop to knock 5% off the purchase price of the car.
For this challenge I personally used the 2011 Bugatti Veyron Super Sport upgraded to S2 level 996.
You can actually knock out 2 challenges at the same time here, the other one is #Forzathon Hyper Fast for just winning any race with a Hypercar.
If you have completed all the Street Races the Town Tear Up street race is the shortest, with load times and everything it took me less than 4 minutes to complete. Video for reference of location of the race, load times edited for brevity.