The SDI info looks right, although I don't think it's fair to dock points for not having 4150 steel in the barrel. They use MIL-B-11595 CMV alloy for their barrels which meets (or exceeds) the milspec for this application. This is the same alloy they use for their M2 BMG barrels and is just about the best barrel steel you can buy.

And the previous poster is correct, SDI M4 rifles sell for ~$1000 for most dealers.