I'd add a vote to the box camera. You clearly already have cameras that will perform, and are looking for some cheap fun (aren't we all?), and the constraints of a box camera add to its charm. I have three that I really like : a Brownie No.2 Model F Portrait version, which takes 120 and has a flip-out lens for close focussing, and two Box Tengors. One takes 6x9, the other 6x4.5. When people see me using them, especially on a tripod, they fall over laughing. Take your family out to the park, like my Dad used to do fifty years ago, and take a picture of them, all posed in their Sunday best, for the family album.
They're great fun.