I'm in Astoria and was looking for a place to fill my tanks too. TechAir on 19th Ave (techair.com) told me it would cost $21 to fill my 10# tank, which is a great price. They also told me that if my tank is expired, they will sell me a new one (filled) on the spot for $26. CO2 is filled while you wait. Not sure what the prices for a 5# would be, but obviously it'd be cheaper than $30.
I called them last week and they said their pump is currently out of order but they expect it to be fixed sometime this month. I have a 10# and a 5#, both empty. In the mean time I'm dosing excel while I wait for them to fix their pump. I haven't been able to find another location, but these guys are nearby and prices/procedure are perfect for me.