Most of the big-name pornstars wouldn't be interested in flying in to do a shoot unless you're a reasonably well known studio with some titles under your belt. What makes them interested isn't how much money you're offering, but how good your distribution is and how likely it is that working for you will make them a big star in the porn world.
Some porn stars supplement their income by offering FS. Their rates are $1200 an hour and up, and you're probably going to be facing a 2 hr minimum. If you have to fly one in, you're probably going to have to pay for business class airfare, a 4+ star hotel, and a day rate for every day of travel.
Sorry I don't recall the name of the website (it was "body-something" I think) but I remember seeing names like Sky Taylor, Lita Chase, Rhylee Richards, etc.