From what I've seen, it's 500 million for an official faction proposal.
As it was in these forums and not the faction creation request, it's probably safe to assume it wasn't an official proposal and if it was, it would have been stated on the proposal.
Yes it is a faction proposal but an un-official one it seems.
So it doesn't need to pay the 500 million, as long as it sits in these forums.
Although the poster should have been more clear at the top of the first post or in the title that it was not a creation request but was a proposal looking for feedback.