Thank you for the insight! I'm getting errors on your links now, though. What do you think of this? Used is around 700.

https://www.amazon.com/Canon-100-400mm-4-5-5-6L-Telephoto-Cameras/dp/B00007GQLS/ref=gp_aw_ybh_a_12?_encoding=UTF8&psc=1&refRID=9CMCGXEG17XW7D29JR09