I know this is last minute and all, but whats the best way for me to gain access to a gilded altar to offer all my bones on?

Gilded altar does not provide double xp. It would be unwise to use bones during the bonus xp weekend as the altar does not work, and if I'm not mistaken actually gives less xp than normal(though that could be wrong but I know for a fact you won't get x2 xp).

 

 

Here it is from the BXPW FAQ

Just in case you're still wondering, go to world 31 yanille, there are almost always people advertising their houses