I don’t accept much paid advertising on this site. However, it is occasionally possible, depending on how long adverts are currently running for. Here are the current rates:
260px x 200px advert on the right-hand side, below the search box
£20/$25 per month for 6 months = £120/$150
150px x 200px advert in the header
£15/$20 per month for 6 months = £90/$120
300px x 200px advert in the header
£25/$35 per month for 6 months = £150/$210