Sounds like your American acquaintance and LatintopXXX could form a team.
First of all Latin could talk the price down to 500B - on the strength of the boy's bunghole being as loose an old woman's.
Then, after they have ridden the boy (like a pony) 3 times each (with internal cumming to keep Mr Yank happy), Latin could call the boy a whore and throw the money on the floor.
I'm sure it would be a hit.
But, to get back to the topic, I'm in agreement with others - the tip should be the same whether its for sex or for other activities.
After all chat could fill an hour whereas it might take only 30 seconds for sex (or is that just me?)