It really depends.
If the virus was a pretty nasty one and couldn't be removed with all the freeware apps out there, I would say you were priced about right (considering what you could have lost if the virus is now really gone) I would probably charge someone off the street about the same to clean an infected PC so I wouldn't feel as if you were scammed by any means. There are, however, some good articles out there(including one on this site!) on how to clean infected PC's. Again though, this all goes back to return on investment (ROI). If you didn't have the time, you had personal data on the PC, and it wasn't your normal malware, good investment. If it was just the run of the mill malware and there was nothing really important on the PC, then you wasted a $100 where you could have also gained some experience. Comes down to a couple factors really.