Do you have pre-installed ducting or would the be the split unit type?
If the split unit, I would advise not to go for the very cheap end as they are very noisy. We found this out to ourcost when trying to sleep at night.
Where you are, there are loads of aircon suppliers. There are several in town and up the road by Iceland. Even places like Aki in the Habaneras and Leroy Merlin in Zenia Boulevard will give you quotes for supply and fitting. Tien21 do the same and are reasonably priced. The inverter type are more expensive to buy but work out cheaper to run as they get to the required temp and switch off until the temp rises. Makes quite a big difference on the electricity bills. You should really be lookin around the 5 to 600 euro range. The cheaper ones are generally not cost effective and noisy.
If you have pre-installed ducting, then the specialist shops plus Garcias (furniture shop) and Don De in Quesada will fit.
Make sure you let them know the size in cubic metres of each room so they can work out the best unit size.