Some Turkish estate agencies should be able to offer you much better rates for both sterling and euro - you should ask if they have a special deal with any banks. I work for a construction company called Wise Move Homes in Altinkum/ Didim, and they for example offer annual mortgage rates of below 6%, due to a special deal they have with a local bank. So make sure you ask for their best rates - check Turkish bank web sites for an idea of where to start negotiating from.