Hello all and happy new year!
I got an update regarding the electronic lock with magnetic keys.
The lock they are using in Athens hackerspace is the cisa elettrika [1]
It is connected with an Arduino that checks the validity of each i-button that every member has. If the i-button is ok then it opens the door through a 12 volt relay.
The i-buttons cost around 2 euros max.

[1] http://www.electriclock.net/acatalog/cisa-elettrika-rim-locks.html
-- 
-p