He is quite hard to get ahold of. And for the nicer top spots, I think it even extends into a few thousand per month. Would recommend sticking to signature spaces + waiting for a following to build around you. Grow the vouches, grow the donator status
OT: You'll have to be able to outbid a current banner holder to get the spot. The bottom ads are significantly less expensive if you want to try those. Pm Sythe if you want to inquire further about bidding someone off their spot.