Need inexpensive tablet to work with Square reader!

[BrrBTR]

I'm setting up a charity event and need an inexpensive tablet to use to take payments with Square (squareup.com).
Their specs say it may or may not work with any given tablet - and that the tablet needs a headset (not audio only) jack.
So, does anyone have experience with square and if so, on what tablets (cheaper is better, since these will be only marginally attended to and might "grow legs").
Or can you tell me how to figure out from online info which tablets have headSET rather than headPHONE jacks...?

Thanks, in advance, for your help!

 

[NateTheGreat]

I know the Kindle Fire can take a headset jack.

I know that's not exactly cheap, but it should work.