So is there some more convenient way for a periodic visitor to SFO to pay for the MUNI in particular?

I have a BART pass for taking the BART from the airport to the hotel downtown, but, my customer is accessible via MUNI only. So everytime I head into the MUNI stations downtown I need to have six quarters, and on the way back I need two quarters plus a single to buy a ticket. That's eight quarters a day for four or five days.