I just looked at the invites in your bio!! Super cute!!!! But....so hopefully you don't feel bad about the price....
I stayed away from square invites due to the extra postage. I went w/ a rectangle pocketfold. It ended up costing me $1.05 per invite (plus the 44 cent response card) because they were too thick.
So don't feel bad about the postage...you might have had to pay the same amount w/ a rectangle anyway.