I think the easiest and the most effective way to market your site is to open up an affiliate program. There are many affiliates that have great sites and they will happily promote your paysite for a cut.

You might contact webmasters running blogs in your niche and tell them that they can make money promoting your stuff. If you have a good content, most of them will not refuse that offer.

I think that it is better to buy ad spots directly from the site owners instead from the networks, but it is more time consuming because you have to contact them directly but you might even get a better deal.

Just look for keywords related to your niche. I would search for terms like “muscle girls” or “female muscles” on Google and try to find some sites. You might also have someone contact you after reading this topic, who knows, there might be webmasters that have such traffic.