The accommodation works out at (we think) 115 Euros per person including tax and the like. This needs to be paid on arrival, or departure, or somewhere in between, they seem a bit vague about it!
Other costs:
Transport to and from the airport in the UK, we'll leave to be sorted out separately among those travelling together.
Car hire and fuel in Spain. We'll just add up the total cost and divide it out equally, either at the end of the week or when we get home.
Food. We'll need to be careful with this to make sure it doesn't get too out of control in terms of who has paid what and who owes what to whom! The best way is probably to have kitties to cover shopping and the like, probably one per house? Whether we cater communally as a (very big) group, or within each house, or whatever, can be decided when we get there and found out exactly what the facilities are like.
David will be doing some shopping as the shops may well be closed when we arrive, and almost certainly on Sunday. We'll just divide the costs of this out equally among us when we get there.
Anything I've forgotten?