Crysmatic - I'm an organic soil outdoor grower so my methods may not be as applicable if you are growing indoors or hydro. What I meant by "how you feed them" if that the manner in which you feed and the frequency that you feed makes a very big difference. Smaller, more regular feedings are better for the plants - it gets more nutrients to them, and you will end up using less fertilizer than you would if you were doing large feedings all at once. Plants use up the majority of the fertilizer they are going to use pretty quickly - within hours from what I have seen. Doing small feedings once a day, or even twice a day, gets you a much higher growth rate than doing it every few days or once a week like some folks do.
Foliar feeding is also hugely important in my opinion. When you foliar feed, far more of the nutrients get used by the plants. When growing in soil only about 5% of the fertilizer you apply via soil drenches actually gets used. When you foliar feed, the amount that gets used is closer to 70-80% if I remember right. Not only that but when you foliar feed, the plant starts using the nutrients immediately. You can correct nutrient imbalances within hours feeding this way. Finally, it takes a lot less fertilizer to foliar feed you plants than it does to do a soil drench. So when you foliar feed, you get more nutrients to the plants, and use very little fertilizer with very little waste. I foliar feed once a week religiously, and you can do it even more if you want. I've been watching one of my friends do an ID run and he has been foliar feeding 3-4 times a week and the plants are the healthiest and fastest growing plants I've ever seen him grow so far.
As far as bulk ag products go, all my soil prep comes from bulk ag. companies. For my compost I have been using products from the company Grab N Grow out of Sonoma county. You can get yards of well made organic compost from them for between $15-$45 a yard, and organic pre-mixed soil for $42 a yard. Last time I checked a yard of
Fox Farm Ocean Forest was almost $1,000 a yard. Look around in your local area and you can probably find good soil company. I live in a big agriculture area, so I look for places that the people running the vineyards and orchards are buying their stuff from rather than the hydro stores. The other things I've been using are gypsum, worm castings, rice hulls, lava rock, and contractor sand - all of which can be purchased in bulk for very cheap, so long as you are buying it from what I would call a "real" ag company rather than a hydro store.
The other big thing I've been doing lately is making my own actively aerated compost teas (AACT.) The AACT's are pretty amazing from what I have seen - they boost nutrient uptake by almost two-fold, and you can replace part of your fertilizer program with them, resulting in less ferts you have to buy. My sap levels doubled after applying it twice over a two week period, and I was using one third less fertilizer. Plus they are dirt cheap to make - it costs me about 50 cents a gallon to brew up - far cheaper than the organic hydro nutrients I use. All the stuff used to make them is cheap and easy to find too. I make mine out of compost or worm castings, Pacific Gro Liquid Fish, seaweed powder, liquid humates, a very small amount of backstrap molasses, sometimes apple juice, and sometimes mycorrhizae spores get added at the end.
For running ferts thru my drip and for foliar feeding I am still using hydro products but at some point I would like to eliminate this. So far though I don't feel like I know enough to start mixing my own nutrients. If you are looking for cheap bulk stuff for this, check out Grow More. I've seen people get amazing growth using their products - BUT they are not organic so I do not use them myself. Grow More works amazingly well though and it is dirt cheap - it is used by many farmers all over the world.