Korean company Joyfriend put on the market a small mp3 player with integrated GPS.

The Joyfriend mp3 player measures 65×110x20mm and features a 128×64px FSTN display. 128MB memory is built-in.
Not quite sure how useful the navigation functionality is on this low-cost mp3 player. It definitely does not support graphical maps.

The JoyFriend mp3 player sells for about $128.