hibid.com
Ive picked up a Swaro Z3 there for $300 and a Zeiss Conquest V4 for $350 at different times.. both in excellent condition..
Be advised, for every great deal I've gotten on hibid on scopes or other firearm related stuff, I've passed on a few hundred... typically stuff goes for "ok" prices, but not "great" once you factor in the buyers premium, shipping and handling, and tax...
Definitely read the fine print with every auction you bid on.. some will charge reasonable or even actual shipping... others will seriously stick it to you on buyers premiums and shipping..
and don't get sucked into a bid war with anyone.. Ive seen used swaros go for almost new/full retail.. because someone just had to have whatever was up for bid..