Isnt it because production car bodies are usually made from metal and so cant have the colour "mixed" into the actual parts?
I think gel coating is part of the body material.
I still could be wrong though
The other way I looked at colouring is that to start with you could leave the car gelcoated and then later down the line once the cars built you could look at spraying - i figured this would save me the money initially.
Don't know how much everyone else is budgeting for the car, but it doesnt seem easy to keep costs near 8k. A safer bet seems 11k!