Car insurance + road license cost - calculator

To answer this question properly you need to provide more information about yourself. Are you an experienced driver? Already have a driver's license in another country? Where are you getting your license in Spain? A rough estimate would be 500 to 1000 Euros and 2 month's time. The first thing you need to check is whether your country has an agreement with Spain that would let your existing license be used here or facilitate getting one without testing.
If not, then you will have to pass a medical exam and both the written and the driving test. You pay a fee (91 euros) which gives you the right of three attempts to pass the two tests. If you don't pass you must pay the fee again for three more attempts. The tests aren't easy. I am a licensed US citizen and there is no agreement with the USA. In my case, I prepared  for the written test by taking sample tests online at the todotest site. You can take these tests over and over again until you pass them all. Since you need to take the driving test in a car equipped with a dual set of pedals, I ended up signing up for a driving school. I went to some classes at the school, and passed the written exam with one error. It wasn't as difficult as I was expecting. I still haven't taken my first driving test, because I lost my TIE, and had to get a copy, which cost me a month of time (You can't take the exam without the TIE)! The school has me signed up for the practical exam for the end of this month, but I will not get a testing slot until after Hogueras (in Alicante), at the end of June. I started studying on todotest in November! I have taken about 15 lessons from the school at 23 euros per 45 minute driving class. Driving in Spain isn't anything like driving in the western US, where I am from, so the class and school are worth it as far as I am concerned. I am very impressed with the whole system, the laws, traffic circles, differences in signage, respect for pedestrians, and the rigor in the testing system. I had to unlearn many things from driving in the US.

Hey Clax thank you very much for your response. Basically I do have Serbian and Maltese (EU) driving license, but I would be registering-insuring car on my girlfriend. She is Spanish, 35 and she has her license for ~17 years. I am more curious about how expenses go up based on engine size / horse power / emissions. In Malta on example almost all of that is irrelevant its just important when the car was imported, so I was curious how that goes here. Thanks again for your time

Jelja

It is very simple.

You or your girlfriend can just call a car dealer in the area where you will live.

The circulation tax (road tax) is determined by the towhall in the area where the vehicle is registered

A car dealer in the area will be able to tell you what the circulation tax will be for the car you will buy.   There can be a considerable difference town to town.  Some small towns I believe make no charge

A dealer will also be able to tell you what buying/ registration, taxes, fees will be and how long the process will take to buy and register a car

Call any insurance company and ask for an insurance quotation.   Later you can shop around to get the best deal

You will then know exactly what the costs will be in your precise circumstances