Say a guy paid a girl to marry him, they fucked, and then got divorced the next day. Could this be counted as prostitution?

Was the money exchanged with the expectation of sex?

Say a guy paid a girl to marry him, they fucked, and then got divorced the next day. Could this be counted as prostitution?

Going off what you said, the money was exchanged purely to get married, what ever happened after they got married is purely coincidental to the law, not guilty!

Besides which the exchange of money for sex isn't strictly unlawful, what may be unlawful depending on which shithole you live in is the activities related to prostitution, such as solicitation, keeping a brothel, etc.

Yeah that might not be prostitution but man that's a serious headache to go through just for one night of paid sex.

Hmm, it could possibly be labeled as seduction
http://criminal-law.freeadvice.com/violent_crimes/seduction_carnal_knowledge.htm

Its defined as when a men lures a women into sex with the promise of marriage, but that's a long shot and no one gets charged with it in the 21st century.

Frankly, I doubt anyone would care if you just handed her 100 bucks and said "suck my dick"

We have governors doing it for Christ sake.
http://www.nytimes.com/2008/03/10/nyregion/10cnd-spitzer.html?ref=nyregion

That's a lot of money. Getting married is not cheap, even with just the service. I would of just done the sex for "free" and then "lose" the money on the road and she would happen to pick it up.

FAIL.

Hmm, it could possibly be labeled as seduction
http://criminal-law.freeadvice.com/violent_crimes/seduction_carnal_knowledge.htm

Its defined as when a men lures a women into sex with the promise of marriage, but that's a long shot and no one gets charged with it in the 21st century.

Frankly, I doubt anyone would care if you just handed her 100 bucks and said "suck my dick"

We have governors doing it for Christ sake.
http://www.nytimes.com/2008/03/10/nyregion/10cnd-spitzer.html?ref=nyregion

But thats if he says "have sex with me, then i'll marry you.", its totally different than saying "marry me, and what ever happens afterwards happens."

In the US, some or most or maybe even all states have laws about length of marriage and when you can get a divorce. I think in my state, you have to stay married at least 6 months before you get a divorce. I'm not even sure where to find that information though and I'm too tired to try.