As a point of comparison, a local guy here in the Bay Area charges $100 hr., but he's really good and worked fast the time I used him to rebuild my exhaust system. You might check with Moyer to see if he can give you any leads to find someone in your area.
What kind of problems are you having? My A-4 has twice had a cut out problem, which I tracked down to a bad coil the first time, and blockage in the carb the other. In trying to troubleshoot the Moyer manual was very helpful, as in each case, the symptoms were different and consistent to the advice in the manual. For example, the time I had a bad coil--the engine would die when I backed down to idle after being run at cruising speed for a while, always coming into the slip, not fun--I was able to diagnose it as an ignition problem. From what I understand, a stuck valve is a common headache too, although I haven't experienced that.