Classic Mustang pre-painted body parts?
Most Mustang parts places do not have prepainted panels (that's a lot of P's). Almost no one wants their replacement steel painted in anything other than primer.
The big problem is panel fit. A lot of times the replacement panel needs some work in order to fit properly. So any painted panel will only be damaged during the installation.
Painting a valance should cost very little, maybe $100 unless its in some funky color. Why not install it, primer it for now, then have it painted later when you have some cash?