If it gives you any idea of what you'll use, I started off with a nearly full 9 litre hobbyweld cylinder , how near full I can't remember, I've emptied that and refilled.
I have marked the gauge on this new cylinder and I'm half way down it, only front bumper bracket areas to do now, perhaps a few bits more.
Initial cost was about a ton deposit , then 35ish for the fill, rough calculation is I'll have used at least one and half, perhaps two if it expires more quickly .
I didn't go for rental because I can't see a time when I won't have it, but I'm unlikely to chomp as much gas as I have done over the past six months.
And if I chuck the towel in on rot fettling I can get my deposit back, less a tenner plus vat handling fee.
But convenience should be high on the list, and If the BOC place ticks that box, then it sounds good to me.