Looking at support as a cost kind of misses the point. Bugs are bugs, and your big-ticket customers might just drop you rather than helping you figure out what is wrong with your product. Ignoring paying customers (even small-time ones) prevents you from improving your product. If they took the time to reach out (and especially if they're paying $100/month for support) you really need to listen to them and try and figure out how you can fix the issue so it won't affect big-ticket customers.