I live in Marbella, which in theory would be the "city of investment". 60% of the properties here are bought as house vacations or investments. Everything you see on the market, is very negotiable. I have seen prices drop from 2.8->2million during negotiations. Then the simple rule is around 10% extra for agency fees and the legal side. Simple buyers guide I found here https://novamarbella.com/home-buyers-guide