Need inexpensive battery with a lot of storage, longevity not important

[AndrewP]

Do you have a Costco nearby?

Their Kirkland deep-cycle (size 27) is ~100 amp-hours and is around $80. I didn't check their warranty but I suspect is at least two years, maybe three (Costco is usually pretty good about this).
If they're anything like my Delco Voyager batteries (and they just may be) they should last at least 5 years easy (I know you said you didn't care about longevity, but if the batteries are still healthy after you're done with them, you could recoup some of their cost by selling or re-purposing them)..

Funny-this is my favorite battery too. A few years ago they are a bargain at $50. They are now about $75 but still a bargain. I get about 4-5 years and replace. I just replaced on in my FJ60 that I bought in 2007, so not too bad.

I run a dual battery only in 1 of my trucks all the others run this Costco battery. It runs the fridge, does starting and winching duty, no real complaints.

The idea of paying $250+ for a fancy Platinum group 31 does not compute for me. In the end, a dead battery is a dead battery.