[totaltec]

First idea that popped into my head was to use variants. Then you could set the price for each combination directly. Seems like a clumsy solution though. I can tell you from experience that altering the price through attributes with custom code is tough. I've done it before and it takes a lot of editing. Mainly because X-Cart checks back with the product to get the price several times throughout the checkout process.

My advice would be to find a way to just add the price through the options without percentages. Clear coat costs $5. Color costs $2. Make the price of the clear coat cover the most expensive combination and don't worry about the minor differences.