Why You do not need to buy new tanks ? There are plenty of great steals out there on tanks, especially aluminum. Don’t worry about the “life saving” crap. It’s a tank and if the valve is good (can be replaced cheaply) and it passed hydro and vis, you are good.
Purchased a used tank with current Vip and Hydro or buy at a slightly higher price under the condition that it passes vip and Hydro if needed. As for regs, I have purchased a few used, but immediately get them services and or rebuilt.
See if your LDS will match or at least come close. Also need to look at the hydro date. Tanks have to be hydroed every five years weather they are used or not. Also older aluminum tanks, depending on the year and manufacturer have the potential cracked necks. Many shops will no longer fill those. Also when a tank is shipped, the valve is supposed to be off the tank, which then requires another visual inspection from a certifed provider, usually a dive shop. How much good will with the LDS are you going to give up by trying to save a few bucks buying online.
Additionally if you are set on aluminum, you should be able to find something manufactured in the 2000’s pretty cheap. Unless you are talking about certain alums that have are made from certain alloy. But that isn’t the age in question but that certain aluminum tanks made at a certain time were made with a faulty allow. I would also try to get a set as the bouancy characteristics vary between manufacturers.
Pay as little as 5 dollars for some of the tanks I use all the time. As long as the first hydro was after 1990 your fine. Also, hydros are much cheaper if you find the place the dive shop takes them to. Welding gas supply places do hydros. I pay 20 a piece and it takes a day.
Bought a new tanks or used tanks from a very few trusted friends, if you dont want to inherit someone else’s problems and you have to know the service history.
That would be my vote. There are always exceptions to the rule, but in this case you will feel great and confident with a shiny new tank. For the long haul you may end up paying much less for servicing, etc.
Sometimes (not always) the cost difference is nominal, but a few extra dollars is worth a few tons of peace of mind. In a sport where one’s life depends on much of the gear used, cutting corners or saving a bit of cash is not always the best approach. Invest in quality.