I work in the 'industry' related to pubs and recently got a 14lb bottle off the delivery driver for £10 to use on my MIG welder.
14lb is the weight of the C02 inside the bottle - unregulated bottle pressure is about 800-1000PSI....!! so yes, a primary reduction reg is required
there are many other suppliers of C02, BOC are about the dearest, some don't even take a lease fee.....
not to worry eh, after all was just a suggestion