Do the trip many times
You can plan the route uising Google Maps and avoid Tolls Roads or use a Sat Nav
They take you down the A67 from Santander
at Osorno go on to A231 to Burgos where you pick up the AP1 E5 to Madrid
at Madrid you go round the East side on M50 and then South of Madrid you join the R3 which takes you down in the direction of Murcia where you follow the signs to Almeria
Close to the junction of M50 and R3 and just off M50 we stay at the Ibis Madrid Arganda which is convenient and relatively cheap-about 4 1/2 hours from Santander and the same to Vera
Most of the journey is very easy but one or two parts can be a little tricky so I would advise using Sat Nav
Can be busy around Madrid but otherwise no problem-generally driving on Sundays are quieter but not sure about August as many Spanish travel south at weekends