My mom gave us a hummingbird feeder, and I stopped at the store to buy the nectar and was shocked by the price. I did a little google search and found that it is simply sugar water. (All the bird sites say to not use any coloring, as it may harm birds, and isn't needed to attract them.)
So to fill your feeder, boil 2 cups water and then whisk in 1/2 cup sugar until dissolved. Let cool, and then fill up your feeder. We have had a huge gathering of hummingbirds since we did this last week. (Unfortunately, the quickest way to make them disappear is to grab a camera.)