If it were me, I will not purchase any tank unless the hydro and VIP are current at least then you know that the tanks have been looked at by a shop or a hydro facility.
I'm a bit up in the air on this one. What would you prefer, tanks that are out of hydro, or tanks that have a few months to a year left on hydro?
IMO, the out of hydro tanks can be more attractive for the following reasons:
1) You're not paying an "in-hydro" price for tanks that are just about to go out of hydro.
2) You can usually get a "refund on fail" condition from the seller. If you buy a tank with any time left on hydro, you're usually in hole, since the seller won't know if the tank was bad when you received it, or if you abused it after purchase. Also, any money you save from not having to get a hydro done now will have to be paid in a few months anyways, with the same uncertainty but without the insurance.
3) On the flipside of 3, You're getting the benefit of a fresh hydro on tanks you otherwise know nothing about, rather than trusting that they've been taken care of over the last 4+ years.
For me, if we're talking 2+ years left on hydro, I'm pretty happy. Anything close to a year left I'd personally only pay out-of-hydro prices, or get the seller to guarantee it passing hydro immediately on purchase.
Also, I've seen various prices for new AL80s lately. I bought two AL80s with 300bar DIN or convertible pro-valves, with brand new hydros and stage rigging kits, for around $100 recently. An LDS near me was just selling brand new AL80s with yoke valves for $99 during a sale last weekend, and I've seen these tanks online from $120-150 regularly across the country.
At those prices, I'd only buy used if I was sure I was getting a really good deal.
