There is a distinct absence of these in most barns. Farmers may allow guests to use the toilet in the house. Similarly you may have to provide the seating and tables. Some farmers, whose barns are used regularly, seem to have supplies of these. Most do not.
Hay bales are an alternative but tend to collapse slowly over the evening.
As with barns, village halls vary from the delightful to the grim. They are normally big enough for most dances and come equipped with tables, chairs, electricity, kitchens, walls and toilets. Prices vary from venue to venue without any clear reason. It is worth shopping around. These venues are ideal for events like weddings and other celebrations where the dance is just part of the celebration.