These blueprints have a good ratio and are easy to build. They are tile-able so you can just add another if you need more steel. From left to right:
1.3 Steel/s - Inputs: Iron Ore 6.6/s (1/2 Yellow Belt), Coal 0.5/s.
2.6 Steel/s - Inputs: Iron Ore 13.3/s (1 Yellow Belt), Coal 1/s.
5.3 Steel/s - Inputs: Iron Ore 26.6/s (1 Red Belt), Coal 1/s.