So the wrist-only ones are more expensive then?
So if you're using it for more low-key activities (walking, sitting, standing), a wrist unit without any motion sensor should work fine, and be pretty decently priced. They get trashed regarding ratings because they really are not effective during real work-outs. But if no other problems are mentioned by reviewers, then that shouldn't be a problem for sedentary ME patients.
Costs for a wrist unit without a motion sensor seem to be US$50-150, whereas ones with a motion sensor are starting around $200. I got a Mio Alpha with motion sensor as a gift which was 150 euros (120 pounds on amazon.co.uk) - I love it, but wouldn't have been able to afford to buy it myself.