You can buy Reddit Avatars with Google play rewards.

FYI You can earn Google Play rewards by downloading Google opinion rewards and doing surveys and uploading receipts. You also get play rewards for anything you buy in the play store and tons of other survey apps. It is usually extremely difficult to use the rewards on anything that is outside the Google ecosystem, so the fact you can get an avatar is pretty surprising.

It's also pretty easy to acrue enough for at least a 10$ avatar between drops IMO. I'm sure a lot of you already knew about this, but just in case.