$130 for a 10# tank, actually, but it's aluminum. He didn't have any steel 10-pounders to give me a price on. He mumbled something about "list price" while he was looking them up, though, so he might have given me the wrong quote.
I'll see if I can't find one cheaper on CraigsList or from the online brew-supply places. My long-term plan is to have a 20# to run a soda fountain, a 10# for beer dispensing, and a second 10# for carbonating/backup. But one step at a time.