How much does it cost you when you exchange the carbonators?

My nearby grocery store (Fred Meyer) just doubled the price of carbonator exchanges, from $15 per tank to $30 per tank. I honestly thought they'd made a mistake at first and were charging me for a new tank, but it was actually the exchange price. I'm going to be checking some of the other places that do exchanges near me to see if they have more reasonable prices and will update here with what I learn.

I looked at SodaStream's site to see about just doing it through them, but at $15/tank and $15 shipping would only work if I was doing several tanks at once each time. Right now, I only have two tanks, so that I have one in the machine while I exchange the other one.