Here's what you're going to need to set up either a 1/2" system:
About 2 feet of 1/2" schedule 40 PVC pipe.
Glue on a 1/2" SLIP x Female threaded coupling to one end. You could probably use a plastic epoxy but I would use PVC cement and primer.
Get a 1/2" male to 1/4" female bushing and screw it into the coupling. That's your barrel. To propel your stuff use an air compressor. Air compressors use 1/4" pipe thread fittings. They make air triggers that have a male thread on it. Screw the barrel onto the trigger.
Fill the barrel, turn on the compressor and test it out. You might have to plug the end with wax or something so the pressure will build up in the barrel a little.
The fittings and pipe will only cost you about a $1.50. The cement goes for $2.49 and the primer is $1.79. That should do it.
Orchard Supply Hardware
Fear not, as there is a way without an air compressor. Use a bike pump. Although, still, if your gonna be a low budget filmmaker, you should get a compressor.