How much for Robot Dice?

Ordered more blank dice and printed up more stickers to make these customized dice for Happy Birthday, Robot! These are well-made plastic dice from Koplow Games with weather-proof vinyl stickers.

I'd like to sell these at GenCon, but I don't know how much I ought to charge. When you factor in the cost of materials per die, it comes out to about a dollar and some change. (Kinda scary, now that I do the math.) I'd like to sell these as sets of three, but I doubt even hardcore GenCon buyers would pay $4 or $5 for three hand-made dice.

After some discussion, looks like I'll first be offering the dice for about $4 for a set of 3, with the purchase of the book being even $30. If no one bites, I'll lower the price, possibly down to free as a promotional item. I'll also be bringing sheets of stickers for $1 for the DIY crowd.
Daniel Solis
Art Director by Day. Game Designer by Night.