Another option is to keep looking at the site near the time as left over tickets from tour groups sometimes become available , I recently bought my ticket a few days before.
Bundle of thanks
yes this is last way, how was your tour? and which other cities you visited?
The tour was interesting. We learned specifically about the old neighborhoods of Albayzín and Sacromonte. It was a lot of uphill climbing up narrow streets until we reached the top of the city, at the same height as the Alhambra and saw great views of it from there! We were mostly in places where there are no cars. After that we got our ticket to go into Alhambra and explore on our own. (More uphill climbing!)