Actually, google says it is. It is, and it isn't. Certain things they do are illegal but paying for sex isn't illegal :|
It's illegal to prostitute with someone under 18. Not sure if that means the prostitute is under-age or the recipient.
It's illegal to be on the strits and solicit sex. So, girls can't walk along the street in skimpy outfits, a car pulls up, they talk and then get in. That's illegal.
Being a Self-employed Prostitute working from home, or working for an agency is ok, as long as the "worker" is 18.
Pimping, running an agency or brothel is illegal - you can't profit from someone else's sex (then what's porn o_O)
So, if you run a website that sells yourself to people for money, it's legal. If you run a business then it's illegal.