The Alhambra is beautiful and really worth a visit. You can see parts of it without tickets but if you want to see the palaces and the wonderful gardens you need them.
Try and book online in advance as the queueing system for buying there is badly organised and can take hours.
This is the official site in English for buying tickets:
tinyurl.com/6hruxo
Updates
Not only that but at many times of year it totally sells out weeks in advance and many unsuspecting visitors miss out. Booking is a must.
Is this your business?