Sorry to bother the OP of this topic, but it might be interesting for him aswell.
I got a gas bottle from an old welder. It was laying in his bench for an unknown time. There's still some gas in it, but I haven't welded with it yet, as I also got a rented bottle that I'm going to use first.
Now, after I read your reply, Toystory, you scared me off a little bit. There's a sticker on the bottle saying "2012". Does that mean I need to buy a new one? Will the gas supplier fill the bottle, or just give me a new one? Do I have to worry about that 2012 sticker?
Is it a good idea to weld with such old gas? Atleast a few years old I guess. The bottle was covered in dust, so yeah.
Once again, sorry to do this in your topic, but it might be interesting for you to know aswell.
Personally, I would go for a bottle you buy. Imagine you rent a bottle for a year. You notice that after 7 months, you don't weld that much anymore and the renting price isn't worth it anymore so you stop the rental and give the bottle back.
If you have a bought bottle, you can always weld and don't have to worry about monthly rental money and other things. If you later decide to stop welding and give you bottle back, you'll get the price of the bottle back aswell.
Just my opinion about this.

Goodluck and have fun with your Christmas present!