I have a feeling the price for accounts will go up with Primedice offering to earn as much as 1BTC for big posters.
A full member should be able to earn 0.4/month with primedice if he posts everyday, 0.1 seems to be a minimum for a good full member account. Good luck on your quest, you may find a seller.
Pretty sure that the Prime Dice signature campaign is for staff members of the forum only.