You can get "concrete sand" from landscaping yards which is very coarse sand plus small grits which will work good as planting medium. However, depending on where the sand came from, it might change your water chemistry.
More expensive, but still 1/3 or less the price of ecocomplete, is Schultz Aquatic soil (or Profile), which is used for pond plants and is guaranteed safe for fish. I get that from my garden center. Disadvantage of Profile is that it has no nutrients, so you have to mix in fertilizers right from the start.
You can use Ecocomplete or other "complete" aquarium plant substrates. It can get expensive quickly. You can save some money by having your plants in pots, or just have an area with the Eco where you are planting & using regular gravel for the rest.