My 2cents..
Be careful with trying to commercialize what was once a hobby. People came to your page, instead of pillowpages because you were an enthusiast, not someone out to make yet another buck off of the working girls.
I originally ripped into the owner of pillowpages for thinking that the web is something to make money from. In talking to her, I realized that she's not the only one. Have you ever looked at the prices that girls pay to be listed in the free-press?
Unfortunately there's still a fair bit of bad taste left (even though it's been years) from the first page (private-eye I think) to attempt this. They were successful in obtaining sign-ups, but left folks high and dry with no return on investment. I don't know the whole story behind that one, but suffice it to say, it soured the market.
I know you want money (hell, we all want money) but trying to get it from your content providers is probably not the best way to do it. And an ad is content. Even those of us who have never used the services of an escort enjoy reading them and dreaming. If you want to make enough to cover hosting, try a paypal donation thingie. You'll never be able to charge your readers (the free press puts out for free), but I'm sure enough of them would appreciate the service enough to donate from time to time.
You're an enthusiast, and you run an enthusiast site. I really used to enjoy using it to window-shop. Hell, I still sorta do..
Don't let the quest for the buck kill you off like it did pillowpages.
Boobies are good. *griN*