Hmmm... I just took another look at those numbers...
60,000 shirts per month = 720,000 a year
$18,000,000 per year / 720,000 shirts = $25 per shirt
Not all their shirts are Select tees, and the (more expensive) hoodies only got one run. It's possible the $18m is based on expected growth over the course of the year, or based on revenue from other streams, but it doesn't seem to quite add up.
$18,000,000 / $15 = 1,200,000 tees = (very) approximately 60% growth over the course of the year. Which I guess is perfectly reasonable since they expect 300% growth in 2006 over 2005. So I guess if it's a projection it does add up, which does make sense.