Hebrew study in Israel

....help!
I'm heading (back!) to the Middle East and planning to spend 6 months in Israel, doing an internship and travelling about. I'd really like to do some Hebrew evening classes while I'm there but I can't seem to find anything except Ulpans aimed for new immigrants... Does anyone know of any good Hebrew schools (preferably in Jerusalem or Tel Aviv) that aren't absurdly expensive? Preferably something I can arrange in advance so I'll have some evidence to show the friendly security people at Ben Gurion... Any help would be very appreciated! cheers