Pete,
We have just bought an property in Calis & have found one question is can be difficult to get answered i.e. What is included in the cost? I am confident all will be well; but I would caution you to get this fully written down before purchase. If you are somewhere with a shared pool for example, who will cover the cost of replacing the pump?
As for costs, this will very for many reasons, including who the builder is. I hope this helps.