I suspect agricultural produce is cheaper in the North, vegetables etc, some prices in supermarkets/shops are also likely to be slightly less expensive since ground rent costs will be cheaper outside Bangkok.

From experience, the cost of living advantage of living outside Bangkok results from the associated lifestyle changes, there are more tempting things to do, interesting places to eat etc in Bangkok. Another area of reduced expense outside of Bangkok is that homeowners are likely to have properties with larger gardens and as a result, spend more time in them rather than spending money at the mall etc.

We were having a similar discussion to this about a week ago over at the other place and I wrote that our average monthly expenses are circa 50k and that my electricity and water bills average 1,300 and 100 baht respectively. We eat as well as anyone would and spend around 10/12k a month on groceries (all in) plus another 10k or so on meals out, we want for nothing and don't restrict ourselves because of budget. Most of that low figure results from lifestyle choices and not having children, others mileage will vary of course. FWIW when we lived in Phuket and rented, our monthly outgoings were typically around 150k.

TBC the 100 baht is solely for showers, laundry and cooking, we use a different source for the garden and outside cleaning.

I was wondering about that, given that you appear to stay in hotels. 

FWIW our drinking water bill is around 50/75 month, based on the season.

Wrong end of the stick in that case, sorry, I'd got the idea into my head that you are a travelling man, a globetrotter of sorts, not to be confused with Rodney of course.

Fme they are the rednecks of Southern Africa, plenty of inbreeding 

It's called 'going tribal'