Seed costs for soybeans are determined by the cost of seed purchased (or saved from the previous crop), seed size (seeds per pound), and seeding rate (per acre). Cost per bag of purchased seed is determined by the seed company based on the supply versus demand of the variety and the cost of producing the variety. Varieties that include a tolerance to a specific herbicide cost more because of the research investment used to develop the variety. Recently released varieties have a greater demand and justify a higher price than older varieties.
Iowa State University
Whigham, Keith, "How to lower soybean seed costs" (1998). Integrated Crop Management News. 2277.