Mine were $350 to get painted. Some of the cost goes towards the prep work before the paint is applied. Because they are flexible, an adhesion promoter needs to be used or the paint could crack and peel over time.
There are paint stores that sell the adhesion promoter and factory color matched paint in aerosol cans, but it is pretty expensive and the results may not be good. Plus there is other prep and chemicals needed. I think that a good body shop is the way to go.
Below are my Bushwacker Extend a Flare.