Well, I'll have some idea of the answer over the next few weeks, having set up an advert for one of my affiliate programs. Not much risk for me, as I took advantage of the $50 free advertising offered by Yahoo to new account holders. Even so, I'm not going to be extravagant - I will take the opportunity to attempt to move from a position of ignorance to a useful level of experience.
Currently I have the max price per click set as low as possible (10c), but I think this will probably have to be raised to get any ads appearing at all. How much experience can I squeeze out of $50 of Yahoo's money and $5 of mine. An encouraging thing is that one sale will net me >300% return. Won't be so easy when I'm not getting my investment multiplied by 11.