Just called Robert's, and they quoted $12 for a 5lb cylinder. But one of my cylinders is past the hydrotest date, and they said it's $15 for a test. They do swaps, though, so really they just swap it out and do the test on their own time. Anyway, refilling 2 5lb cylinders and a hydrotest will cost me $39 plus tax. Not a bad deal, and better than the local AirGas. I'll ask about 10- and 20lb cylinders while I'm there.
Thats not too bad. Cost me about $32 to refill my 10# at a hombrewing store here in Raleigh. I think the last time I was in there I filled both of my 10# tanks with tax for around $72.