guidance on price for selling a lens

Hi, just seeking some guidance on a fair selling price for a Sigma 70-200 EX HSM F2.8 zoom lens. It's the non-DG version, bought March 2005.
I've never sold anything before, and realize you can't sell at, what you paid for. But I have no idea whats fair to ask, or when I'm being taken for to low. How do lenses depreciate, time, condition,..

In my opinion, the lens could be put back in it's box, and sold as new, far as condition goes.

Anyhow, guess I'm just looking for some ballpark/fair dollar fiqure to work with in my head. New to photography at the time of purchase, I see now I overpaid for it.

sorry Mods if this is the wrong forum to ask, I didn't want to post in "For sale", as I'm looking into selling.

also, CyberDyneSystems, you were right, advised me long ago 70-200 wouldn't have the reach for Soccer, you suggested the 100-400. I've rented it, love it, and it's my current mission. Big change from U10G - U12G.

At its cheapest B&H had it for $714 new. I would say used in mint condition should fetch around $550-$600. The price increase on the new macro version should make this lens more apealing to someone on a budget.

Put it on eBay for 10 days and let the market sort it out. Works for me.

Ballpark, ebay would get you 65-85% of new price.

thanks, $550-600 (American) gives me something to work with. Just wanted some idea where to start, don't want to give it away, and don't to ask for to much either.
thanks for the eBay tip too, I myself don't look for anything on there, but my wife always is. If eBay is the way to go, all the better, she can handle it

One thing I've found with eBay is that one needs to resist the urge to start the bidding too high. Start it low to suck people in. Don't worry, it'll get bid up to fair value. I also like to start 10 day auctions on a Friday. That way the auction covers two weekends and I get a lot more views.