When we put in a supply to our barn conversion we hired a digger and did all the trench work ourselves to spec. They even gave us the cable to lay in and all they did was come out, inspect what we had done, connected it at each end and supervised the back fill and warning tape etc. This was a while ago but it cost very little, a couple or 3 grand I think.
On the subject of planning, my advice would be to link it in some way to some form of enterprise, especially if you can provide even temporary work to others. There is now a presumption in favour of sustainable develpoment and what that really means is that you have to show that you are bringing productivity and hopefully employment to your bit of the countryside. If you can throw in some form of public ammenity, even better. The best approach would be to do up a business plan showing why you need each cabin and why you need to live on site.
Just buying a field and expecting to get a house on it is pie in the sky in most parts of the UK I'm afraid. I have a field which would be a dream place for a cabin and we are trying to plan out how we can do the above within the regulations. As a parish councillor, I can't just bung one up and go for certificate of lawfullness in 10 years time, tempting though it is. On that note, the law has been changed on this so that a certificate can be refused even after 10 years if the planners can show that you have deliberately concealed the breach (like putting it inside a barn or planting high trees all around it and then cutting them down after 10 years, so take care on that on. It's a new rule so not any precedents yet I believe.
As for planners being envious busy bodies, I can see why people think that and surely some are but many are fair, decent people. My motivation for joining the council was not so much to tell people what to do, it was more to make sure we didn't get a council or people who had only moved into the parish 6 months ago. Our primary aim is to keep our nose out of people's business as much as possible.
My final point would be that these cabins are stunning and I can see the appeal. But. 20 or so years ago, my Dad gave up farming in a big way and sold off a huge chunk of the farm. Many fields around us have ended up as 'smallholdings' or just people putting caravans, yurts, cabins or whatever on them and to be honest, 90% of these places look like junk yards and are a disgrace and there is little or nothing anyone can do. You cannot blame the planners for not wanting to see this all over the countryside. People dream of owning a couple acres and usually it ends up as a dumping ground with the mandatory shipping container, a knackered Landy and a few rotten tarps floating around the place.