Nate,
Take look at the content label on any bottle of fertilizer. Notice the items listed in the highest percentage. Especially the N-P-K. Go to anywhere, search for the individual components. For instance, a 5lb bag of FeSO4 costs about $25. Lasts forever and is a good for foliar applications. Depending on your type of culture and water you may or may not need to consider micronutrients. But that stuff at cvs.