The most versatile I can think of is the Cycle Satiator by Grin Tech http://ebikes.ca
, but is definitely not cheaper. However, it's very programmable (on-unit or via USB) and is weathersealed and vibration resistant. You can use presets for each of your batteries and simply select from the menu which one to use each time you charge a pack.
More affordably, but also weathersealed/vibration resistant, though not programmable, there are adjustable LED PSUs that can be used as chargers, but they are nto designed as them, so don't have some of the safety shutoffs/etc, like Meanwell HLG-x00H-xxA from 100w on up to 600w (maybe more) versions, up to at least 54-58v output and up to at least 10-12A. You'd have to use a multimeter to monitor them while you adjusted the voltage and current, as they have no inbuilt display for that. Also you'd have to do this adjsutment manually (with a screwdriver) for each different pack voltage you want to charge (12s, 13s, 14s, etc).