That sounds right, $500.00 for 30 more horsepower. That is how company's think. You are probably right, the only difference is the cam, sounds crazy buy people see 290 instead of 260 and they want the one with more horsepower.
I don't live in Phoenix, but I have always just visited shops, asked for references, and then did a little digging around myself to see if they have some or a lot of bad reviews. 1 or 2 bad reviews in say 10 or 15 years in business is going to happen, but several is always a bad sign.