I have a new Cobra 9MM Derringer that had one of those BAD pulls you hear about. He put in a lighter trigger and hammer spring, polished the sears, trigger & hammer. Charged $30 ~ said the polishing took the majority of the labor ~ 5 Minutes time! I suppose it's according to what you've got, parts needed, and the complexity of the dis-assembly and re-assembly. I think he got the springs out of a "spring box" he had on hand and replaced my springs for them. I was happy, going from a 27# to an 8# pull and it still goes bang every time! Reasonably accurate now on a paper plate at up to 10 yards.
That little fella you've got is light! Also, you might want to get a parts list and see if it has springs or not. Also check on how hard it is to take apart. There may be Wolff Springs available for it. Wolff sure helped the pull on our SP101!