GGGEEEZZZ, I was afraid getting my CO2 tank(s) filled would be a pain &/or a ripoff. However, guess I got lucky and AirGas in SLC, UT filled my 5# for $6 total!
Another to place to try might be an auto parts store if they keep Oxy and Acet for the shops. I work for an auto parts store that exchanges airgas tanks and its about $24 out the door for 20lb. Never check hydros, open 7 days a week, and I believe cheaper than going straight to airgas!
I swapped my 20# tank and 5# tank out at Airgas in Orlando FL two weeks ago, It was $38 after tax for both. I did not pay attention to the individual price and this was my first time doing a swap. Normally I go to a local package store where they fill the tanks.