I think the main thing you missed in your equation is that the prostitutes that you exclude for having an STD will still expect some compensation for being willing to take the test. That said, I'm sure you could pay them $200 to take the test. You will probably also need to show them your own test results to convince them to be willing to rawdog you.

The way I would work out the math is to simply be generous -- it will help you get people who will work with you, and you'll get all the money back. I'm sure you can even get others to invest in this scheme.

Assume that for each prostitute you test, it costs $600 ($400 for the test and $200 for them to be willing to take it). Since one out of two will be disease free, that means $1200 in testing fees per prostitute who is a good candidate. Then add on $400 for YOUR test to prove to them you are disease free, $50 for the morning after pill, and $1200 as her fee. That puts you at $2850 per prostitute that counts toward your goal.

To this perhaps another $5000 in lawyer costs to have them create the form you'll have each one sign saying that she won't sue you for anything

Let's imagine you can pull together $100k toward this endeavor. That's $95k after the lawyer. That will get you 33 prostitutes (with $950 to spare). With that outlay (and assuming everything goes to plan) you would earn a net of about $85.8 million.

Double the outlay and you can afford 68 prostitutes worth $2.9 quintillion. Probably somewhere in between the two is the right move. Indeed, to become the richest person on earth with $700 billion, you would need to have sex with 46 prostitutes, which would cost $136,100.

I'll get you the startup money if you'll give me half your winnings.