Power Amp Repair Question

Just wonder how best to proceed in my situation. I took my McCormack Micro Power Drive to a repair shop one month ago. They had a $100 estimate fee and I assumed I'd get an estimate with a diagnosis. After one month, the shop doesn't know what's wrong but says I lose the $100 if I want it back. I asked if they might know in 2 more weeks and they said probably not. So, how long is it reasonable to wait? 2 months? More? Is it fair to ask for the estimate fee when there's no diagnosis or estimate after one month?

Thanks,
Ron