They are around $13 IIRC - You should fill them with well carbonated beer as the CO2 charge will dispense the beer but not much more, according to a couple of guys who have tried them, that I talked to at BABBs.
Edit; so you want a CB brewed beer in them? (just twigged to your OP) - run out of beer ???
Why not pick up a cube of the same brew and do it yourself?