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spadout.com will compare most major (as well as not so major) retailed. For example, type Black Diamond Momentum AL Harness and it will sort results by price.
mountainproject.com has an amazing For Sale forum, where great deals can be scored
cascadeclimbers.com has a Yard Sale forum that also frequently has good stuff.
I just unloaded several hundred dollars of extra climbing gear but have a bit left. I have an extra #4 Camalot (new with tags) that I would part with for $65, as well as some shoes and alpine pants.
I own more gear than your local REI, and have gotten most of it on sale. Happy to help with any climbing related questions!