Walmart does sell several different cases I tried a couple and returned them and then I bit the Bullet for a hard-shell folio by Zagg includes builin Bluetooth keyboard and has the magnets that put Ipad into sleep mode when you close the cover as I recall it's around $99.00 but the cheaper ones just didn't work well for me. also the cheap ones seemed to have trouble maintaining the link between keyboard and Ipad the Zagg has been flawless.
Yes, Walmart offer covers and cases for Ipads but be carefull because sizes for previous models are too big for Ipad air. Even, I think inches reported in this page are wrong because instead of 11.3 x 3.6 x 9.4 my Ipad air has: 9.5 x 0.25 x 6.625, so when I tried to buy one case on my local store it results too big (apparently associates didn't know about this changes). Now I'm trying to get that specifically designed for this model.