riddle...

a man tries to buy a one-of-a-kind pair of shoes
from you and you ask him what he will offer.
at first, he observes the shoes and stares into
your eyes to come up with a number. he reluctantly
says, "i'll give you $1 for the shoes." of course,
you are not amused and sweat rolls down the man's
face due to the fact that he has said the wrong number.
however, he really wants the shoes, so again he offers.
"$50" he says. you think that much is good enough for
a normal pair of shoes, but these are no normal shoes.
"$500!" he squeals. at this, you say nothing, because
you are shocked at how great the offer is. fortunately
for you, he takes your silence as disapproval and shouts,
"$1,000!!!" is this guy made of money? you wonder.
pleased with the previous inflation, you say to him,
"i'll give you the shoes only if your next offer is
similar to the ones you've made so far." what does
the man unexpectedly offer you next?