I am a person who has trouble focusing on work and fidgets a lot. I work on the computer frequently. I figure treadmill desks might cure this. Also, it's cold and icy where I live and if I can get my older family members to walk or run around more, it will be good for them, so treadmills are a good investment for removing trivial inconveniences..

Should I buy a cheapest possible treadmill and just put a stool on top of my desk to create a standing desk?

Should I buy a nice expensive regular treadmill, and use it for desking and running?

Should I buy the (expensive) treadmills specifically designed for treadmill desking, and only use it for desking?

Other options?