Did you look at the Niagara Cycle Works link I posted? You can get a fork there for a little over $20, likely less than $30 even with shipping.

You need to know the length and diameter (likely 1" in this case) of your steerer tube in order to get the right size. I'm assuming this is a 26" wheeled bike. You can get away with a longer tube length but you'll need to cut away a portion of the tube and possibly have it the tube threaded down further (an LBS job). The right length makes your life much easier.