Pay per click ad function

Hi there.
I’m looking for a free or paid-for plugin that will allow my customers to either:

A: Buy credits for their advert to appear, and once it has been clicked X number of times, the ad will be removed and them and me alerted (so more credits can be bought)

or

B: Same as above, but an invoice sent out after so many clicks have been registered. i.e., customers do not pay in advance.

Thanks for your time and help.

Harty.