I am looking for a good platform on which to build an advertising site. I would like to configure it so that users can place simple ads (text, image), which will be uploaded to their industry section. Something like community classifieds. It will be mainly for businesses. I would also like to edit these ads if needed. Would also need it to be extensible, so that I will be able to charge for an ad. depending on various criteria (position on the page, size), but for now it will all be free.
I am open to using php or asp.net technology.