I found a solution that is simple and works for me. So I thought I'd share it here in case others are in need of a cheap cup holder.
I found this magnet cup holder on Amazon. It works. So simple.
Here is a pic of two on my ZTR. I had just got them and transporting one over to the tractor.

Link to Amazon:
I found this magnet cup holder on Amazon. It works. So simple.
Here is a pic of two on my ZTR. I had just got them and transporting one over to the tractor.

Link to Amazon: