depends on how much you use, small volumes may be rent free but you pay a deposit for the cylinder, or for larger volumes you pay and annual rental but the gas cost is smaller, one you decide which way to go you can start to see what suppliers are arround for you
Apparntly SDL Minorfern, Castleford, WF10 4SB, 01977800300 stock Hobby Weld, who do Argon. I've not used them yet, but there listed on the Hobby Weld website.