Not a flap, rather an aileron, but I had to replace one on a -7. Parts costs are straightforward to get from Van's, then add in labor and paint. For labor, I included all of the following (how much time on each, and the labor rate, is an exercise for the person doing the work):
Removal
Parts fab
Fitment, match drill, debur
Dimple, prep, prime
Rivet stiffeners
Assembly and riveting
Installation
Test flight
Removal for paint
Installation post-paint, test flight
As noted, plus parts costs, plus paint cost.
YMMV