[Edited after the Early Bird Special ran out]
When the $549 Cosmo Early Bird Special Perk began running low, PC added a $599 Cosmo Special Perk, with no limited number.
Thus it seems to be like this:
750 x $549 Cosmo Early Bird Specials (a 31% discount), all gone now.
Unlimited $599 Cosmo Specials (a 25% discount), likely during the rest of the crowdfunding phase.
Unlimited $1098 Pack of 2 Cosmos (a 31% discount), likely during the rest of the crowdfunding phase.
Unlimited $2745 Pack of 5 Cosmos (a 31% discount), likely during the rest of the crowdfunding phase.
So, to get the 31% discount, team up with one or four friends to get one of the larger packs.
Or, if money is no object, go for the $1999 gold plated Cosmo (still a tad cheaper than a 512GB iPhone XS Max)
At first I found it a tad odd that buying 5 would give the same discount as buying 2 (or one Early Bird). I can only guess the idea is to make it possible to buy any number, except one or three, 31%-discounted Cosmos during the entire crowdfunding, by combining lots of 2 and 5. A pack-of-three instead of five would have allowed any number, but would you like, say 30 (new communicators for your sales force maybe?) you'd have to place ten orders (rather than six).