I get swap refills at the welding shop. Sure the bottles are ugly but I've never had to pay for a hydrotest.
I recommend getting the biggest bottle you can. I pay $20 to fill a 50 pound tank delivered to my office. Once my 20 pound tank goes dry(been 2 years now) I'll hook up the big one and probably die before it does. 20 pounds costs $12, 5 pounds costs $10 and my 2 pound traveling bottle costs $8.
Build a relationship with them and it pays off. The welding shop didn't have a 5 pound tank swap one day so they gave me another 20 pounder. Somebody left a 2 pounder there and never came back for it so they gave it to me since there's no market for a bottle that small