If you have StraightTalk service, or use it for a few months, you can go to their "shop phones" section and find cheap low spec smartphones for free or $10 or $20 depending on how low your standards are. The catch is that you buy one month's service with it. Since my wife uses StraightTalk I just buy a service card that way every once in awhile instead of online, and get the phone along with it.

BTW get a Google Voice number, set up Hangouts and install Hangouts Dialer, and you have free wifi-only phone service.