If you are are looking for a UK holiday with low cost accommodation then a mobile home at one of Haven Holidays sites could be the solution. They are offering half price holidays for many dates except school holidays and bank holidays. There are different grades of mobile home, from basic (but still with shower, toilet and fully equipped kitchen) to deluxe.
I have stayed at many Haven sites when our sons were young. One of our favourites was Hafan y Mor near Pwhelli in north Wales. The countryside around the area is really beautiful. There is a site at Berwick upon Tweed, my new home town. If you would like to visit Edinburgh there is Seaton Sands, on the coast in East Lothian, with a direct bus service into Edinburgh city centre.