For your "cheapest" battery, call around to your local battery shops (specialty shops, not places like Walmart) and ask if they have any "blemished batteries" that will fit.

If a battery sits on the shelf long enough to lose it's initial charge it can no longer be sold as a new battery, typically the shop will scrape off the sticker, brand the top of the battery with a literal branding iron that says BLEM, then sell it for half price as a blemished battery with no warranty and no sticker. Sometimes it's just a battery that got a huge scratch across the sticker from mishandling but I've always ended up with discharge blems, the shop does recharge the battery though.

Basically you're ending up with a 2 year old battery for half price, I've used dozens over the year on vehicles that just needed a battery for cheap.

Group 24 is about 1.5 inches longer than a group 35. I think it does fit in the box but I've never actually tried, I replaced mine with the OEM group 35.