Membership costs probably vary from city to city and franchise to franchise.
Go talk to the people at your local Curves. They have lots of different prices. Get them to let you try it a couple of times for free. Make sure the curves is not to crowded during the times when you want to exercize. I would stay away from long term contracts, even though there is usually a price break. Remember, they make money from selling memberships. You have to pay even when you don't work out.