The best source of these fertilizers in my area is Hieden Feed and Supply on Stuebner Airline Road. I was able to pick up two 50-lb sack of cottonseed meal for $14.75 each ($0.30/lb), and one 40-lb sack of MicroLife 6-2-4 for $25.95 ($0.65/lb). I hauled it all home and mixed it up in an old 55-gallon steel drum (mouse-proof), and added just a little garden sulfur to help with soil pH. The final mix made approximately 30 gallons, or 480 cups of fertilizer, costing around $0.12 per cup. I have somewhere around 50 trees and plants, so this works out to be a very economical way to fertilize and add organic matter to the soil.
According to the EPA, the average N-P-K of cottonseed meal is approximately 6-2-1, and the N-P-K of Microlife 6-2-4 is 6-2-4. By combining 100 pounds of cottonseed meal with 40 pounds of Microlife, I wound up with a 6-2-2 mix. MicroLife is great fertilizer, but this hardly seems worth the extra cost of the MicroLife. I'm told that MicroLife also contains lots of other micronutrients and minerals, but since I also mulch and supplement with composted kitchen scraps, I'm probably already getting these.
The next time I go for fertilizer, I'll probably just get cottonseed meal. Considering the cost difference, it would be cheaper to add more cottonseed meal per tree than to buy the MicroLife. Leave a comment and let me know what experience you've had with different fertilizers.