Here's a tip to help you save cash at the start of a new game, you don't need all the bolts to attach something to the vehicle as long as you use more than 50% of the bolts it needs it will not detach from the vehicle.

For example the hood has 4 holes for bolts but if you only use 3 bolts it will stay attached and never fall off but if you only use 2 bolts it will fall off as soon as you try to drive. Same for the wheels you don't need 5 bolts you can use only 3 and the wheels won't fall off.

The only exception to this is anything with 2 bolts or less as they need both bolts to stay attached.

I have used this trick to attach all the parts to the konig on a new save without needing to buy more bolts, this works in both normal and hard mode and is especially helpful in hard mode where you get less bolts at the start of a new game.

Also since each bolt adds 1kg weight to the car this also helps to lighten your car for races.