In case you still need that information since your post is nearly a month old:
The main carrier is
ALMERAYA . At least for covering Almeria-Madrid, so it´s a good guess that
ALMERAYA is also the main carrier for Madrid-Almeria.
The buses leave from Madrid, Estacion Sur de Autobuses, 5 times a day. The schedule is as follows:
09:30 15:00 18:30 22:30 24:00
The return fare is €37,-- (more or less), one-way aound €19,--.
It shouldn´t take more than 8 or 9 hours to get to Almeria.
Hope this helps.
Jesus