As with everything else, it depends on the region, the church size, service time (peak or off-peak), whether/how much they value the instrument, and a few other variables.
In Atlanta, the "average" would be about $125-$150/week. But if you factored in every single church in Atlanta and surveyed them to get a real average (total salary of hired drummers divided by total number of hired drummers), it would probably be about $25/wk or less because you have a lot of churches that don't pay at all, or pay very little.