You should check out the official Alhambra web site
here. By clicking through to "Alhambra Tours" and then to "Regular Guided Tours", you get to
this web page. You'll see that the regular guided tour is 49 Euros, not 90.
That's the tour we took in September '07. It was a very good tour, with a knowledgeable guide, and they even picked you up and dropped you off at your hotel. So in that sense, it was worth the price.
Still, I ended up wishing we had just paid for general admission and the self-guided tape recorder. Why? The Alhambra has 4 separate and equally beautiful areas to see and visit. When you get tickets for the Alhambra, whether via general admission or via a tour guide, you get a separate ticket for each. Each separate ticket is valid for exactly one entry. As with any tour, they go at a steady pace, whether you'd rather explore that area further or not. The problem is, when the tour is done and you'd like to go back to the areas you're interested in, you
can't, because you've used the ticket for that area.
I understand the necessity of this policy, due to the huge number of visitors they receive each year. But it makes the guided tour much less practical than you'd think.
-Bob