Yeah, how much does it cost to advertise your affiliate links or banners on someones website? Has anybody done this before?
The cost to advertise on a website will differ from website to website. If they don't have a page that talks about their advertising rates and available ad positions, try contacting the webmaster to see if he would be interested in selling you ad space.
Yeah, like Activeweb said, the cost to advertise on any website is whatever that website charges. So you run the numbers and see if the expected affiliate conversions pay for the cost of the ad. It's just like buying PPC ads for an affiliate link. (Except in this case, you could be giving your competitor a good idea, and they might run their own affiliate link instead.)