Back in the day, Ratts, people would take off to Wales, buy a run-down with ground, and renovate it. Everyone's on to that now though.
A field will only have agricultural value, therefore cheap. To get PP to site a mobile is a hell of a job. I tried for someone a few years ago. You have to show that the enterprise (business) taking place on the land, has to be capable of sustaining you, and necessitates you living on the premises.
If a field has PP for a dwelling, you could pay 2,3,4 maybe 500k for it....... depending on where it is.
I have seen smallholdings/horsey/horticultural properties come up locally, with a mobile already sited......... still 250k range though.
I would suggest a search agent. A friend of mine does this for Stags. I'm not sure if Stags are in Bideford, but certainly in Barnstaple.
Might be worth registering.