Organic fertilizers don't have to be expensive, since you can make your own. If you buy the components in bulk, you'll save even more!
Recipe For Organic Fertilizer
I've been using this recipe, which to the best of my knowledge was created by Steve Solomon (founder of Territorial Seed Company), for six years now with good results. One word of advice: Instead of buying the components in small boxes, buy bulk bags (40-50 lbs.) at a farm supply or feed store. As long as you keep them dry, they will last for many years.
All measurements are in terms of volume, not weight.
4 parts seed meal
1 part dolomite lime
½ part bone meal -or- 1 part soft rock phosphate
½ part kelp meal
This component provides nitrogen, with smaller amounts of phosphorus and potassium. I like to use cottonseed meal, which is cheap (about $13.00 for a 40 lb bag) and easily available. In some states, though, it is not allowed in a certified organic operation (not something a home grower needs to be concerned about). Other options are alfalfa meal, or rape/canola meal. Cottonseed meal has a NPK value of around 6-2-1.
In spring I like to substitute blood meal in place of some seed meal, since blood meal is somewhat faster acting. Try using three parts seed meal and one part blood meal.
Seed meals tend to be acidic, so lime is included to balance that out. Dolomite limestone is roughly half Magnesium Carbonate and half Calcium Carbonate. Calcitic limestone is pure Calcium Carbonate. Plants usually need more calcium than magnesium; so, if you want to be really tricky, use 1/3 part dolomite lime and 2/3 part calcitic lime.
If your soil is alkaline, you might experiment with reducing or eliminating the lime in this mix.
Bone Meal And Rock Phosphate
These ingredients make up the bulk of the phosphorus component. Less bone meal (NPK ~ 0-10-0) is required since it releases its phosphorus more readily. The advantage of using rock phosphate (NPK ~ 0-3-0) is that it continues to contribute phosphorus to your soil over many years.
I like to use bone meal. Not only is it easier to find, but also it is already being produced as a byproduct of the beef industry. Rock phosphate is mined. Twenty pounds of bone meal will run about $5.00.
Kelp meal (NPK ~ 0-0-10) contributes potassium, and also many micronutrients. This tends to be more expensive than the other components: I recently paid $35.00 for a 50 pound bag.
Another possible potassium source is Jersey Greensand. It has the same advantages and liabilities as rock phosphate (it's very slow release). In addition, it does not supply micronutrients.