Carbon steel I-beams are the most affordable, typically $10 – $30 per foot. Galvanized I-beams, coated to resist corrosion, generally cost 10 – 25% more due to the zinc coating process. Stainless steel I-beams are the most expensive, often 2–3 times the price of carbon steel because of their high corrosion resistance and polished finish. Choosing the right type depends on your environment and durability needs.