I bought a used iPad Pro 10.5 for $280 off eBay. I’ve seen others in the 270-300 range. I find it to be a good deal. Obviously a new one with a new battery and perfect shape is preferable but i was pleasantly surprised.
I find the best way to find a good deal is set up a saved search for “iPad,” set the search filters and maximum price, and buy it now only. check back a few times a day using the app and you’ll find a great deal within 2 weeks.
if you want one that’s in great cosmetic shape and are willing to spend more, I know of a particular seller that has them. PM me for the name. I have no relationship to them. But have bought 2 iPads in the past with great results.
they sell them for $320 for iPad Pro 10.5 or Mini 5, $380 for Air 3, and $550 for Pro 11 (all base models)