LP85 or Al80?

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$60 is a very good price for a steel 72, especially if it is galvanized.

For a new tank, the LP85 is the closest in physical size modern tank to the venerable old steel 72. It's only 1/10" larger in diameter and just barely longer. Due to slightly thicker walls, the LP85 has slightly better buoyancy for most people, at least if not diving without a suit. They also have a slightly higher fill pressure so it's like a LP72 with a "legal" overfill. IMHO, either is a step up from an AL80 and they are my 2 favorite LP tanks for singles.

Still, I prefer HP steel tanks over LP steel tanks. The FX71 (actually closer to 72CF at rated fill) is a super nice compact tank and only 6.74" diameter. For more capacity, I usually recommend skipping the HP80 except for short divers and would go directly to the HP100. Slightly smaller than an AL 80 and with better buoyancy. If under-fills are common, an HP100 will still hold as much air as an AL80 if filled to 2640psi.

And at a somewhat more acceptable 3000 psi in that HP100, you are looking at 87 cu ft.