Amazon $100 Omnibus at a rare 45% preorder discount is $55 (plus 6% tax is $58.30 for many states)
CGN $100 Omnibus at 50% discount is $50 plus $6.99 shipping is $56.99.
So, Amazon has a fighting chance against CGN at the $100MRSP price point, but that's with an unusually high discount on Amazon. Any less discount or any more than $100MSRP and CGN is still the winner.
I'd probably go up to $10 shipping with CGN before I got annoyed. Have you ever noticed how much they pay to ship those double-wide boxes? Mine are usually close to $20!