Fire supply/welding supply should be able to hydrotest it for you, allowing you to use it for another 5 years. My local place charged $20 last time I had to do one.
I called a local welding supply place (Maine Oxy) today to ask about the price of 20# CO2 tanks and the refill cost. I was told $89+/- for the cylinder and $22+/- for the CO2 and refills. So I drove there to pick up two 20# tanks. When the guy at the counter said that it would be $400+, I said "What, I called earlier and was told it would be $112 per tank." Apparently the guy I spoke to on the phone has been working there for two days, and quoted the price for 5# cylinders and CO2 fills, even though I had clearly said 20#. The guy at the counter was nice and said that if I could find a used 20# tank on FB Marketplace, Craigslist, etc. that he would swap it out as long as it has the DOT stamp and is labeled for what gas it contained, even if it was an O2, N2, etc. That was nice of him, but there's virtually nothing available locally at the moment in term of used tanks. Looking online, there are refurbished and tested 20# CO2 tanks available for far less, which have the DOT stamp, but don't have a CO2 sticker, because they are refurbished and empty. The 5# CO2 tanks that they carried locally were tall and slim (~24" tall x 3.5" diameter), which seems like a horrible idea, in that it would need to be strapped to something upright at all times.
Needless to say, I was really disappointed in their actual pricing, compared to what I was told on the phone. I want two CO2 tanks. I would be fine with say a 20# and a 5# tank, as long as they are easy to refill locally and as long as the 5# tank isn't that ridiculously slim tank. I would have had no problem spending roughly $225 for a pair of filled 20# tanks, which is what I drove to get. It no doubt varies greatly by location, but what do people recommend?
I want the ability to keep kegs at standard dispensing pressures. I also want to be able to use a second tank/regulator to push higher pressures to carbonate beer for drinking, or to have a second tank to use when when bringing kegs to events at friend's houses. For the latter, a 5# tank may be nice, but I would have been fine with a pair of 20# tanks.
Some of the larger gas exchange outfits (think Airgas, Praxair sorts of joints) will exchange/swap tanks regardless of hydrotest status. It's another option if you're not attached to your specific tank.
I was planning on calling Airgas this morning, and just did. Their prices were a bit more reasonable than Maine Oxy. For 20# tanks, you can lease a tank for $30 per year or purchase for around $150. Either way, they do a tank swap when you need a refill, which is about $22. A 5# tank can be purchased for around $100, including the initial fill.My experience with Airgas is that they will take your expired tank in exchange if it has an Airgas sticker on it. Otherwise, they'll offer to charge you some additional amount (about the same as a hydro-test fee, IIRC), take your exchange, and give you a tank that has their sticker.
When the guy at the counter said that it would be $400+, I said "What, I called earlier and was told it would be $112 per tank."
I looked at refurbished tanks online as well. Some were as cheap as $59, not including shipping, although that would probably end up being more than the $89 you paid. I didn't check out eBay yet. The guy at Maine Oxy said that the tanks needed to be DOT certified and have stickers showing what gas they contain. The refurbished tanks don't appear to have stickers, which is to be expected if they haven't been filled since being refurbished. It seems like I should be able to swap in those refurbished tanks, but I'll need to check with the gas suppliers.I ended up buying "refurbished" 20lb tanks on eBay, one for $78 and one for $89 including shipping. They are no problem to ship empty. My local gas supplier swapped them out for the usual $18 swap price with no hassle. Now that I have tanks with stickers from my local supplier, they will do swaps even if they go out of date without charging the hydro fee since they are "their" tanks. They will fill "my" tanks if I drop them off by COB Friday for fill by their CO2 delivery truck on Saturday morning but then I'm responsible for keeping them certified.
I had the same situation last year; bought some used kegs from a friend of a friend, he had a 20# tank that he let me have for $10 (!!!). It had "property of coca-cola" all over it in bright red with some legal mumbo-jumbo basically saying if we catch you with our tank we'll sue the pants off you. Some lighter fluid took that right off because I was paranoid, took it to my local gas shop and they exchanged without even looking at it. As I recall it was way out of date too. I get my 20's (I now have two, got another one with a used kegerator later last year) exchanged for $28 at the same shop, my LHBS wants $45.I've picked up several used 20#ers for very cheap on Craig's list and FB that are out of date, one was painted with an old Pepsi logo and stamped prop of Pepsi. Never had Airgas even look at cert dates. They also haven't cared when I've brought them a siphon tank and asked to change to a non-siphon.