I think the site could have quite a bit of potential if someone hasn't done it already.
So pretty much its ebay, except its exclusively for people who want to sell advertisement spots?
One question though about it, for "contract period", is that saying that the bid is placed, which is a one-time payment and then the person will advertise for you for that duration?
I recommend some sort of alternate bidding system, not so its just 1 payment but so you can also have a way so you can charge per click on the ad.
