An authorized Sigma dealer has the Sigma Contemporary 100-400mm f/5-6.3 DG OS HSM for $649 (Reg $799) until 11:59PM EST, Sunday January 28, 2018.
This is the lowest price we've seen from an authorized retailer.
Sigma Contemporary 100-400mm f/5-6.3 DG OS HSM $649 (Reg $799)