Although such a tiny ass space is not worth 50BTC for just a week, I'd totally recommend doing this long term Theymos. I'd pay a steady 5 BTC a week (along with the rest of the people here) for a rotation with even 30 other ads. But 50? You guys are nuts. It costs less than that to run a full color add on somethingAwful for 2 weeks, and there userbase is over a million.
It's an auction. The price will go only as high as people are willing to pay.
This is the bitcoin forum, with a userbase which might not be larger than somethingAwful's, but I can guarantee more people here know what bitcoins are and are willing to check out what's on the other end of the ad link. *That* is why the advertising here is so attractive to people.