Happened across this thread as I was looking for a CO2 source. Made a few calls and here is what I found for local CO2 prices at this time:
Praxair (just off Hwy 101 near BMW) - do not fill on site, cylinder exchange only
5# cylinder ~$20
20# cylinder - $32.37
National Welders Supply (1125 White Horse Road) - will fill on site (may take a day) or cylinder exchange
5# ~ $21
Machine & Welding Supply (519 Old Easley Highway) - - will fill on site or cylinder exchange
5# ~ $10
20# ~ $13
All of the above fill with beverage grade CO2.
I know where I'm going next time!!