I love my service/repair/fabric store. If you buy your machine from them, the first cleaing is free. All other times it's been about $50 for each of my 5 different machines. Parts are extra of course but only the blade on my serger has needed replacing and that was only $3. The family (3 generations) that manage & work there are the kindness, most personable people you could ever want to spend time with. They even do a maintenance workshop for our guild every few years and you learn so much from them during it.
Not sure what they did for you but I'd be looking for another shop. Just my opinion.