Difficult question as there are so many out there. Some (and you will have seen the fly posters all around) install one unit for 250 euros but these will be generally be very noisy and expensive to run. You can pay up to 5,000 euro to get a house fully fitted.
However, you say you live in Dona Pepa II. I think most of these properties have the ducting pre-installed. Check that out first and you can get one (or maybe 2-usually one upstairs and one downstairs) hidden away and are very quiet and quite cheap to run. Make sure you get the inverter type as these switch off and on when the correct temperature is reached instead of working all the time.
If you haven't got pre-installation (you can check if you have air vents in each room) then the split air ones for around 600 euro a unit (fitted) is probably what you need. Have a look at Don De by the arches. Once you have the type, go to other aircon installers as Don De are quite expensive (but one of the best for neat, tidy installations).
There really are tons of different types out there so you need to work out the area to be served (size of rooms) and check you get the one most suitable for your property.