I have no idea about tours since we generally avoid any kind of tours. But, if we were in your position we would probably just rent a car for the day and drive ourselves to Granada. There are extensive parking lots just outside the Alhambra and I understand you can buy tickets in advance via the internet.
casavaha, I don't about the feasibility of touring the Alhambra from Almeria, but I do know that you should get tickets in advance. Don't expect to get tickets the day of your visit. It's a beautiful place. I'd go there again in a heartbeat.