http://www.airbnb.com/rooms/162702
Apartments like this could be an option for people. I like that you get a kitchen and a living room, it might be more comfortable for people staying in Zagreb for a while.
There's also a Best Western in Zagreb. Maybe you could book a block and get wedding rates at a hotel like this (or another hotel).

http://www.tripadvisor.com/Hotel_Review-g294454-d551017-Reviews-BEST_WESTERN_PREMIER_Hotel_Astoria-Zagreb.html