This topic comes up frequently.
Remember, because you can buy it for $50 does not mean that's what it'll cost you to have someone drive to your location, in a fully insured vehicle stocked with tools and supplies, to diagnose and repair your problem. There's a HUGE amount of cost to keep the business doors open, and trucks on the road.
If the problem is fixed, and the performance of the machine is well, then you didn't get ripped off. You had a proper service call.