Well, I'm fairly certain his minimum order is 15 shirts. I had thought of 3 possibilities.
1) Sell the shirts at cost to whoever wants one, like the ones for the Batfish currently.
2) Sell the shirts at cost + a little extra that would be sent to whatever sub museum the buyer designates.
3) Sell the shirts at cost + a little extra that would go towards the payment for this website/forum.
I figure they'd end up costing $8 to $12 each base cost. Maybe $3 to $5 could be put in on top for #2/#3 option. I dunno. I guess it'd all depend upon the response.