My DH got the mug on the 8/23 cruise. He paid $9.99 for the mug and 22 oz refills were charged at the 16 oz price of $3.50. So it took 10 refills to break even. He refilled more than 10 timed in the week, and got a nice souvenir out of the mug, so he felt it was more than worth the price he paid.
He also like that each time he got a refill, they exchanged his mug for a new frosted mug.