The top tier carbon frames are ~600-800g.
Mid-tier carbon frames are usually 800-1200g.
Entry level carbon is 1200-1400g.

The lightest Al frames are ~1200g.
Basic Al frames are ~1600g.

The lightest steel frames are ~1200g.
Most production frames are 1800-2400g.

As you can see there's some significant overlap. High-end carbon is clearly the lightest, but once you're out of the uber-bike category its much more mixed. Keep in that a ~1400g steel frame will cost more than a ~1400g Al frame, and probably a 1400g carbon frame. In terms of kg/$, light-weight Aluminum (like a CAAD10) are the best buy.