I doubt its price will be higher than the Canon L one... It would not be a great marketing idea.
I'd happily assume Sigma came up with this lens when Canon introduced the 24-70/4, which Sigma probably interpreted as "the 24-105 is EOL". Of course Sigma wants that piece of the market. I don't think they care about the 24-105 price, they'll just want to undercut the 24-70/4 (and the Nikkor).
It's good to know that even if Canon retires the 24-105, there'll be an equivalent lens (well, sort of) but I'd still be very reluctant because of AF issues. I'd like to see that change, these folks are putting out a lot of nice glass lately.