A best bet is the refurbished Sigma 50-150mm f2.8 EX DC APO HSM II Lens for Canon (pictured) model no. 691101, for $559 with free shipping. (It's the lens on the top right.) That's $440 under the lowest total price we could find for a new unit. It features a Hyper Sonic Motor for silent, high-speed auto-focus and is designed to work with smaller chip APS-c cameras only.