First, buying used devices is risky and you need to be careful about where the device is purchased from.
If you purchase a used iPad from an unknown or untrusted source, you may get a device that has Activation Lock and in most caes like this, iOS Activation Lock cannot be defeated or circumvented and you end up with a dead, useless paperweight of a device.
I only mentioned used devices as some potential buyers/user insist on going this route. You have to be careful purchasing used Apple mobile devices from truly unknown and untrusted sources.
All of Apple's current iPad lineup all run the latest iPadOS 13.
Older iPads like the iPad Air 2 and iPad Mini 4, as well as, older 2015-2017 iPad Pro models all run iPadOS.
Also, the 2017 iPad 5th and 6th generation can run iPadOS 13.
The 2017 5th gen iPad cannot use the Apple Pencil, but the 6th gen iPad can.
You can find Apple certified refurbished and discounted iPads from Apple here.
Refurbished iPad - Apple
Amazon, itself, also sells all the newest iPads both new and refurbished and older model iPads ( some new or refurbished (“renewed” ) for significant discount, also.
Amazon, itself, currently sells new, sealed in box, Apple's base model 2019, 7th gen, 10.2 inch screen, WiFi ONLY 32 and 128 GBs iPad models selling for $279 and $359, respectively, through its own direct sales distribution.
This is a $50-$70 savings from Apple's own pricing of these iPad models.
https://www.amazon.com/gp/product/B07XQYPM2N?pf_rd_p=ab873d20-a0ca-439b-ac45-cd78f07a84d8&pf_rd_r=6HW54HFD0YSC2ZE3CP7Z
Amazon even has the 7th gen iPad even cheaper for slightly used or slightly damaged models.
The damaged models appear to just have damage to the packaging or missing some of the internal packaging items.
These used/damaged devices can be found after the initial description in a blue colored link labelled “new and used” ( either from Amazon directly or from other Amazon marketplace resellers )
So, you can even save more money on an Apple iPad.
Amazon will also provide for purchase of extended, AppleCare+ product warranty protection plan, also.
Amazon, itself, also, sell other current, newest Apple iPad models at a substantial discount, as well!
New 2019 iPad Air 3
https://www.amazon.com/gp/product/B07PP3Z9PB?pf_rd_r=QZ8DHRKVKQBKCKJPFPPN&pf_rd_p=ab873d20-a0ca-439b-ac45-cd78f07a84d8&th=1
Get the largest iPad storage devices you can afford as internal iPad storage is NOT expandable.
Best of Luck to You!