That sounds high, but it might have been reasonable in the context of the conditions, which I do not know. Maybe your bike was difficult to take apart or put back together. Maybe it was a minimum charge. I would expect to see a charge of $5 to $15, but I can't say you necessarily got ripped off. They have overhead, and they're also taking a risk by fixing your bike for money, so all of those things have value.

It's true they could have done it for free, and my LBS often does stuff like this for free, but they could also do a ton of work like that for free, which would put them out of business. If you haven't developed a relationship with them yet, this might be a good time to start. They won't mind at all if you buy tools from them, and they may teach you how to do it. They will know that you'll be back with more complicated jobs even if you can adjust your own cones. And see if you can buy some tires, tubes, water bottles, computers, and clothing from them. The premium won't be terribly high, and they'll appreciate the patronage. The only water bottles I buy have my LBS's logo on them. I enjoy spreading their name around.