What are some of the average costs per square of asphalt versus metal roofing?

Asphalt roofing can run from $43 to $70 per square (10 ft x 10 ft). This is for felt paper and shingles only (no labor). Button caps (hold down the felt), roofing nails, drip edge and valley flashing would still need to be figured but these are the small portion of the total cost. Warranty ranges from 20 to 30 years at these price ranges.
Steel roofing will also vary by the design and steel gauge (thickness). Normally this comes 3 feet wide and can be ordered to whatever length needed. Steel is also a commodity so the price can vary from day to day. As a rough ball park estimate figure on $2.50 to $3.00 per foot of length. That would figure to be $0.83 to $1.00 per square foot. Warranty is normally 20 - 25 years on painted metal.