Hi Miss Kitty :wave
I'm not really sure about this either, or how any of the technical aspects would be handled (the legalities etc., I'm not very business-minded) -- but I do know that it's very common these days for sites to find one or more ways to let visitors assist in supporting the site financially.......
I just did a quick search in Google asking that question out-right -- I tried posting the link, but it didn't take, so instead try typing in "how much to charge advertisers on a web site" without the quotes, and you'll get several hits.
These two seemed informative right away:
davesite.com and
workz.com
Not much, but it's a start......hopefully the more knowledgable folks here will see this and offer some better help