If you go in Spain, here I speak in particular of Andalusia, and you don't like to stay in the same place all the time, what you need is to rent a car, or a moped if you have to make small trips as in the case of the islands. My experience led me to rent a car for an itinerant holiday in Andalusia, a journey of a thousand km divided into 2 settimane.
If we think of car rental in Italy, it comes to put your hands in your hair and give up the project, given the often unsustainable costs. But Spain is not Italy, and it is certainly more suited to a low-cost tourism compared to our home. Just a simple search on the internet and you will see how the prices offered by online agencies (in my case DoYouSpain.com), which offer cars owned by car rental companies (Hertz, Avis, etc.) at really advantageous conditions: 11 days of rental, with 100 km per day included and civil liability included, have cost me 220€, aboard a dignified Chevrolet Spark (5 seats and luggage compartment for 2-3 hand luggage); having to leave the car always out on the street, I found it convenient to also add full insurance coverage (theft, fire, damage) for others € 60 in total.
The policies on the fuel, who here charge for the first tank filled by them (it costs more than making it yourself, but starting from the airport and having to make your way immediately, the service can also be convenient) and ask that the car be returned empty, even because they do not refund residual fuel.
I add a small but important consideration on the choice of the car: in the trunk size consider not only the liters of capacity, but above all how this capacity is arranged; in fact you are not always able to put your luggage inside (although the capacity may be higher than what you need), and this becomes a big issue when you have to make intermediate stops. Possibly uncomfortable but better than risking theft in your car, consider leaving with non-rigid luggage, putting clothes and towels on the rear seats and crushing the suitcases to fit them in the trunk. A full baggage can tempt an attacker, a towel or a pair of socks much less.
