When in a similar situation, I have sometimes used the B&B organisation run by Farmstay.
http://www.farmstay.co.uk/
These are B&Bs on working farms, mostly large farmhouses in rural areas or the edge of towns. Because many of their customers are families who generally want Friday/Saturday night accommodation, I have found them particularly amenable to negotiating long-term rates based on 4 nights per week - Monday-Thursday.
You can search a specific areas off the website.
It is run in conjunction with the National Farmers Union.