The easiest way to do this is by selling some of the vehicles that you've earned from recovery missions. When you sell a vehicle you don't lose any money, the sell price is the same as the buy price (the law of conservation of energy).
As you do not lose any money you can simply buy back the same vehicles at no financial loss, or better yet in the early stages of the game, buy a much more capable truck.
Any equipped attachments are sold at the same time as the vehicle (also at the buy price). And you can sell individual attachments that are unequipped too, so don't hold off till you unlock the very best tyres. Buy and sell as needed.