If your intention is to produce nutrient-dense food on a scale that means a great deal to the family economy, do a soil test, and amend the soil in the direction that maximizes nutritional outcomes. That’s the best way. Thinking just in terms of money, if you’re growing a large enough garden that its output makes a financial difference, and if its fertilization requires the purchase of anything at all, your annual cost and do a soil test first? Then you can buy only what the garden really needs. The test could save you more than its cost. And if you think of it in terms of your family’s health, there is no choice at all.