Search for Orange Pi, Banana Pi, Pine64 and FriendlyElec. These companies offer a wide range of $10-$30 dollar single board computers based on Allwinner or Rockchip SOCs (most of which include a Mali GPU).

You can run ARM based Linux distros on them (such as Armbian). Up to now, most people use the ARM proprietary blobs to get OpenGL ES acceleration working on those things.