I know of a pro shop that happens to be where I live close to and bowl 3 leagues in and they charge 30 bucks for the price of the labor of drilling if you buy the ball there. The prices for the balls are not great but not bad.
But however, the fact that they charge 20 bucks extra (50 dollars) for bringing in a ball from outside that is not purchased in the proshop pisses me off so for that reason I do not have my equipment drilled there anymore. I'd rather drive 50 miles outside of town to save 20 bucks because it's the prinipal. Screw pro shops that charge extra for bringing balls you didn't buy from them!