Heck yeah I'd buy a used battery if the price is right. Though I probably wouldn't buy one without using one of those $20-ish battery load testers to check it, or having the presumably reputable parts/battery store selling it do it in front of me.
A local salvage yard sells used for $20-$30 depending on size, plus core. The available batteries are on a rack right there and you can look them over and check the dates and put your own tester on if you want. The last battery I got there had a date of a year or so old, and its cca tests higher than its rating. $20 vs. the same battery new at a discount store for $120 vs. the same battery new at a battery store for $180.
Also, I'm sure people here would pay attention, but sometimes "new" batteries in stores can have surprisingly old dates on them.
Someone mentioned Walmart and a certain battery size. Yeah, it must be a very common size or something, because that one, maybe two or three, size batteries are awfully cheap there compared to most of them.
