As far as fertilizing, I would recommend using water soluble fertilizer (easy to put out). Prices on fertilizer have increased and seem to still be increasing somewhat. For a four acre pond I would say 160 pounds of fertilizer would get you through the year. The cost of that much fertilizer would be $320 +/- around here in Georgia. Of course all of this depends on how much water is flowing through the lake, alkalinity levels, etc. If the lake needs to be limed then that is another cost.

For a feeding program you will have to consider the price of a feeder and cost of feed. As far as how much food you put out per feeding, I would not get to scientific about it and just feed enough food so that the fish can clean up all of the food within 5-15 minutes. As far as how much food you will need that all depends on how often you feed. In some areas of the country fish may feed actively for 10 months out of the year or only 5-6 months. So by the time you buy a feeder and food it will be more expensive than fertilizing (considering the pond does not need to be limed).

If your goal is trophy bass, I highly recommend feeding and fertilizing. To have a trophy bass fishery you are going to need more than bluegill. Having a fertile pond will allow you to have a good threadfin population and eventually gizzard shad. If have a good bluegill population along with tilapia, threadfin shad, gizzard shad, etc. those bass should be putting on some serious weight once you get the bass population thinned out and back in balance. So for a trophy bass fishery if the budget allows, I would feed and fertilize. Could go on and on about this subject but need to get back to work.

You can't judge a fish by looking at the pond--Bo Diddley