Jenne - Well I work for a University and I am also a graduate student. So I pay for a membership at the University gym. Its about 230 for the whole year... which is pretty cheap. I am guessing thats probably not an option for you.
A friend of mine's mother owns a Curves. So I am a bit biased, but I would recommend it if you want lots of support and like group activities.
As for getting discounts on gym memberships, you could always bounce from gym to gym and take their trial offers or big discounts for new members.
Another idea is to see if you have a YMCA.. I have heard good things about them.. but it probably depend on where you live.
As for if its worth it? Well if you use the membership a lot it will be

Perhaps it will be a motivator.. cause if you don't use it.. its a waste of money.