I assume the $50 includes not only battery but replacement of the seals and pressure testing as well. Including it in the cost of a battery replacement is standard practice for most companies
Oak (as usual) has your correct answer.
Local shops are hit and miss. Say away from the "mall jewelers" and find a local repeatable jeweler. I have seen several watches come back ruined by local shops because for $10 they weren't caring to reseal the gasket correctly (even saw one where they didn't but a gasket back in at all).