a padded mailer or cardboard CD mailer is 25¢ or less, probably signifiagnetly less in bulk. first class postage on that is probably 80¢ to $1
and "priority mail" on something you wait weeks to ship is just silly.
and first class mail is hardly the same as throwing it to a rock and throwing it in the general direction. after all, that will get there in the same truck that brings the priority mail.
i expect you're using the USPS mailer boxes because they're 'free" but end up costing each member who elects to take that route several dollars more. sure, it's not even enough to buy a happy meal, but it all adds up.
as far as your claim of "not overselling", i'm sorry, when you don't allow anyone who's not gold or higher to use PM, or sell in the exchange, that's a fairly strong selling point for the membership.
so, it seems to me you've either got poor math skills, poor problem solving skills or just don't give a shit when you're spending other people's money.
like i said before, i was gonna buy the gold membership until i saw the extra charges. yeah, it's only a few bucks more, but i'm a cheap bastard. +4% for paypal is one thing, +20% is too beauceaup.