Recruit someone, on a contracting basis, for $15 / hour, to do support responses. Pay that person 70 or 80 hours per month. Adjust the hourly as desirable to get the kind of person you need.

Have that person also build a very comprehensive FAQ, if one does not exist. They can also process any time consuming sales routines for you (refunds, billing questions, whatever). If they're any good at basic sales, you can give them a commission for selling which might get their income up to near full-time after a while.

Begin slightly restricting what kind of support tickets you'll handle (specifically begin to make it abundantly clear to users that if their question is in the FAQ, all you're going to get is pointed to the FAQ; ratchet that up to whatever degree is necessary).