Organic fertilizers, properly applied, will be less expensive then any synthetic fertilizer. However if you assume you need to add the same amount of an organic fertilizer as a sythetic you can spend much more money.
What does your soil need?
What did a soil test tell you was necessary?
Keep in mind that the purveyors of synthetic fertilizers tel you to apply way too much because your grasses will not be able to use most of what you apply and then those synthetic fertilizers cause pollution.

Keep in mind that many things can be used as organic fertilizers. It doesn't have to be something that comes in a bag labeled "Fertilizer" to be used as a fertilizer. Many people use grains like soybean meal, cracked corn, etc or alfalfa pellets. Or coffee grounds from Starbucks (although coffee grounds are impractical in a large area because it takes a lot to provide enough nitrogen.

treenut, what do you use your yard for? Is it just an appearance yard or is it used for sports or other activities? You might consider moving to grasses which do not require any fertilizer. bpgreen can give you a list of them. In fact there is a thread over on the regular lawn forum discussing grass in the high desert. Check it out.

I fertilize with ordinary corn meal bought in brown, 50-pound bags from the feed store. Any ground up nut, bean, seed, or grain will work as an organic fertilizer. The application rate is 10-20 pounds per 1,000 square feet. You can use more if your budget allows, but that amount will get you going. Commercially bagged fertilizers cost 6x more than brown bag stuff.

Where do you live? Zone 8 is not enough information.