I buy my bottles/gas from Arcet on pantation since I may go weeks at a time without using them. The down side is that if you buy the tanks instead of leasing them you can only get the little tanks (dunno what the capacity is so I just call them "the little ones"). Since I bought my tanks from them when I need more gas I return the empty and pick up a full bottle which costs ~$30.

If you do a lot of welding or cutting and forsee needing refills on a regular basis then leasing them may be the way to go. When leasing you can get the bigger bottles too which saves making multiple trips for refills if you use a lot. Its been a while since I talked to them about pricing when leasing but it seems like it was ~$115 per year to lease plus the cost of the gas.

My shielding gas for my MIG and my TIG lasts quite a while which isnt bad as far as cost but I go through acet/oxy pretty quick when using the torch so if I get into a project where Im doing a lot of burning the little tanks dont last long. Just to give you an ideas I went through two of the small tanks of acet/oxy just to cut up the shell and frame of a car I parted out so I could haul it to cycle systems.

IMO the best thing to do would be to call them and get some pricing then crunch the numbers to see if leasing or buying would be best for you.