$35 to assess damage is fair if that include providing an estimate price for the complete repair. If MOSFETs need to be replaced, just make sure they use the exact same part number or if not, provide you with the new part number so you can do our own research to make sure they are in fact suitable replacements. In some circuitry, they may need to be replaced in matched pairs in order to preserve optimum sound quality. Based on the described condition of the unit, I think it will be a minor repair with few damaged parts. Again, what is that purple thing, is it just some tool, tapes that is not part of the amp?