For example, over on the Purchase page, the first round of badges looks like this:

This means that there were 800 memberships avaliable for $30. Once those are sold out, the next round looks like this:

Which means we have 900 memberships avaliable for $40.
So the earlier you purchase your membership, the better the odds are that you'll get a lower price. If you require further assistance, please email Member Registration.