I agree - CafePress is expensive. But as you state, there really aren't any known good alternatives that are cheaper.
Random thought- you think ThinkGeek would be interested in some sort of a deal?
I don't see any point in worrying about it or trying to optimize anything.
If the point is to create public awareness of Wikipedia, its presence on the Internet (and frequency of appearance in Google search results) is probably a (pause for serious numeric estimation) million times more effective than wearing T-shirts. If the point is to support Wikipedia, why on earth would I buy a $20 T-shirt worth $10 in order to give Wikipedia $5, as opposed to a) donating $20 via PayPal (same cost to me, four times the benefit to WIkipedia) or b) donating $5 via PayPal (same benefit to Wikipedia, one quarter the cost to me)?
The only reason for having Wikipedia-logo merchandise is as a service to those who actually _want_ to wear Wikipedia on their sleeve, as it were. Cafepress serves that function adequately.
Wiki-merchandise will never be a significant factor in Wikipedia's financing unless there is a major diversion of someone's time and attention from encyclopedia-building to merchandise creation and marketing.
(But what do I know? I was raised by a mom who never allowed advertising within the sphere of her personal space. No containers of cream were ever placed on the table; the cream was always poured first into a pitcher. The idea of staring at Elsie, the Borden cow on the breakfast table was anathema to her. No bumper stickers on the Smith family car!)
-- Daniel P. B. Smith, dpbsmith@verizon.net "Elinor Goulding Smith's Great Big Messy Book" is now back in print! Sample chapter at http://world.std.com/~dpbsmith/messy.html Buy it at http://www.amazon.com/exec/obidos/ASIN/1403314063/