The car has to conform to Spanish law so most UK cars will need Headlights cganged over, and Fog light if only one fitted.
Car has to undergo Spanish MOT which is the ITV this costs quite a bit for the first one as the test produces the spanish equivelent of the log book and associated paperwork
After the ITV the car has to be imported the cost varies and is based on value of vehicle. Can be very expensive
Also vehicle has to be taxed in Alhama about 90€
I imported a Small campervan and used a broker to do all the legwork, and arranging, i just drove car to ITV and the broker did all the talking. I had to pay the ITV before the test think it was 200 pus tax and also had to pay Tax and Brokers fees and import duty.
It is possible to do it all yourself if you have time and a little spanish? but probably better to get it done via a broker then if there is any comeback you can sort with them.
If the vehicle is not a common vehicle you will almost certainly need a broker to sort.
There are plenty of Brokers around. and compared to the import tax their fee is minimal,
Import tax is very high and poor new car sales do not help.
Mick