That's less than 500 a day on average
Remember you get coach loads making the the pilgrimage up the steps to the Buddha
So 15000 a month not so far fetched maybe
As for the charging that's another subject that really pisses me off
I always ask how the Thais how they would feel if we charged 10x as much to enter our tourist attractions
In fact maybe that's what the rest of the world should do?
Even got my driving licensce so I could get into places for Thai prices, but they don't accept that know
So when I take my 4 kids out on a trek it's costing me 1000bt plus and that is taking the piss!