With data plan. Looking for something smaller sized that easily fits in a backpack and has at least an 8 hour battery life and option to attach keyboard.

Is it Costco or other big box store best place to purchase?

Probably, best bet is to just do some googling and see. Sales are pretty rare for the newer models but you might occasionally catch a deal at Best Buy or somewhere similar.

The iPad Air is pretty dang capable now, if you don't need the upgraded cameras that would probably do you. Can always go with the Pro if you want to future proof a bit.

Found a good deal on an Ipad pro on Woot the other day - $850 for a 2tb 11" M1 model.

Thanks.