I just exchanged a 5lb tank at a local "oxygen" house here in town. It was quite a bit more than I expected. I paid $14.65.
Now, here is the kicker and I don't mind paying the difference. I took in a steel tank and they only had aluminum. So, I definitely got lucky, but I'm wondering if he charged me for my "luck."
Primary: Pale Ale w/ Wyeast American Ale
Primary: Pale Ale w/ Wyeast Northwest Ale
Keg: American Wheat 3 Floyds Gumballhead clone
Keg: Bombastic IPA
tapped Keg: Wild Child Mild Brown Ale
tapped Keg: Hearts Squared - all grain Bell's clone