It does also mention when looking up about the stadium that tickets are available from the stadium on the day. Might be better off to wait until then and see if they are cheaper as the prices on their website are crazy! unless it is easy to join as a member of course
I am horrifically jealous however the below may be useful - Only 65 left on here apparently
http://www.viagogo.co.uk/Sports-Tickets/Football/Spanish-Premier-League/UD-Las-Palmas-Tickets