I set my feeder to feed only once in the morning, so my 30gal. drum last for quite a while before I have to re-fill it. Food plot seed is quite expensive, then you add fertilizer and herbicides , and its quite a bit of coin, not to mention time consuming.
Of course we are comparing apples and oranges when it comes to food plots and feeders. Your plot will surely attract more deer, but a feeder is just another method, but on a much smaller scale. The nice part, is that you can get the deer to stop and feed at your feeder which is in the woods, before they get to the open fields to eat. I believe nervous deer feel more safe in the woods, than being in an open field.