This guide is fairly simple and the best part is, it doesnt require too much work. All you need is a lot of Car Mastery Points (which are super easy to earn especially during Skill Songs) and a little bit of cash to ensure you can get what you need.
Earning Easy Super Spins for Quick Money/Quick Unlocks
Pick any car you want, doesnt really matter, though preferable to use one of the Forza Edition Cars that give you skill boosts for Destruction, Drifting ect. But it doesnt really matter. Go around and build up a Skill Score and get it high as you can so you can earn plenty of Car Mastery Points. (You will need a lot if you want lots of unlocks (minimum of 5 Car Mastery Points needed).
Buy the Willy Jeep (Costs 40k Credits each). You can buy it 1st through the Autoshop but afterwards its faster if you unlock it via the Car Collectible List (But it can get confusing which happens when you order too many.This is why I just order them from Autoshop and put different skins on them to differentiate.).
Get in the Willy Jeep. Use your Car Mastery Points (Only costs 5 if you do it right) to reach the Super Spin. Pray and Hope you get the goods.
Recycle the Willy Jeep and Repeat Steps 1-4. Profit and enjoy all the unlockables.
This method is the best way I find so far to earn easy Cash and earn fast unlocks. Willy Jeep is pretty affordable and 5 Car Mastery Points is nothing for a Super Spin. Plus, With Skill Songs active, Its super easy to get fast Car Mastery. The Most difficult part of this guide is simply finding a good location to maintain your skill score so you bank big points to level up quickly.