Seeki.eu lists 10+ properties for sale and 7+ to rent in Costitx.
The median asking price is €625,000, or €2,797 per m² on a typical 203 m², across sale listings that publish both a price and a floor area.
On the rental side, the median asking rent for a house is €1,500 a month, across house rentals that publish both a price and a floor area.
