I had my frame for my 74 project powdered coated about 3 years ago, there regular price started at $550.00. I live around Sac. CA. so depending on where you live it might be a little less.
Make sure if you go this route that you check into the reputation of the shop. But be afraid to ask questions or tell them you want it to bake a little longer. I have seen a lot of powdered coated things before and if the prep and baking process as Zeig pointed out is not done right, it will be worse than if you just did it yourself.
The good thing is if they do it right it will last for a very long time.