The prices of construction are about 30 to 40 % higher in Formentera than on mainland Spain the two main factors influencing this hike in cost are transport of materials and lodging cost both of which impact the construction price.
Alot of the work is done by immigrants which for the most part are semi legal (they don't have a NIE) in the country these will ask form 7 to 13 Euros an hour. But be aware that if you are caught employing a person which dos not have social insurance YOU and not him will be fined up to 30 000 Euros per person.
Stone Walls
Stone wall work only 1m X 1m X 60cm from 60 to 70 Euros (this dos not include stones or cement) and the price goes up if the height exceeds 1.5m.
You can expect to pay about 25 Euros per m3 of stone and add about 45 Euros for transport as well as 39 Euros for the loading.
Notes:
There are different styles of stone wall building, the original Formentera style uses stones taken from the land which are practically not worked with the stone hammer unfortunately unless you have stones on your land or buy old stones you will have to revert to buying stones which have been quarried these have to be extensively worked and ake walls which give a less natural aspect which I refer to as the Arab style.
Water Cistern
You can roughly expect to pay 200 Euros per M3 of cistern
Notes:
To calculate the size of your water cistern assume a daily water consumption not including garden watering of about 120 per day per person .
To be Updated