Old Android cell phones are cheap..  If you want the people to get phones start doing a cell phone donation program. how many people do you know that have old and still perfectly useable cell phones tucked in a drawer somewhere?

you can put the phones in Wifi only mode and use them as pocket tablets. if you just need them for the wallet app any old Android phone running 2.3 (gingerbread) and up will work for that application.

basically...
Team up with electronics recyclers, cell phone shops, and electronics stores. Ask you fellow geeks and co-workers. you should not have any trouble getting a few hundred phones donated.