I thought about replacing the battery. Nice to hear that $99 would be enough to cover that (I'm assuming that includes shipping it to Apple, along with parts and labor)! In the end, I ended up getting a 9th gen iPad. It's over 3x the price, but we do get an iPad that's in new condition, the latest generation, somewhat larger screen, and latest version of iOS (I would've been fine with 1 or 2 generations past if it was a used device for a good price TBH). Spec-wise, it pales in comparison to the Air and Pro lines, but those are also much more costly. I'm just using my iPad as a more basic+ gaming device, so those would've been overkillI decided to replace the battery in my iPad Air last spring. It was $99 and while that probably wasn't fiscally prudent, it would have served my needs ... which is basically reading comic books.
Decided to get an OEM replacement at the Apple Store since the local "fixit" places were charging the same price and Apple just swaps it with a refurb unit. I figured, what the Hell.
It took a long time because they didn't have any replacement units available and had to order it from HQ. When it did finally show up (after some nagging by me), I ended up with an iPad (2017) as the replacement unit. Bumped up from 16GB to 32GB as well.
Not sure if iPad Air is still on the list for allowable service, but you might end up with a better iPad.
YMMV