How much is a second-hand Nikon D80 nowadays?

I'm thinking of selling mine to upgrade.

Well, without seeing/testing the camera, it is hard to say… I know, everyone on the internet is really honest (especially when they say "It looks and functions like brand new:"). That is why I don't buy off of ebay anymore.

I would suggest you take it into your local camera shops and ask them to give you a "trade-in price" and a "buying price". Normally, the "trade-in" price will be slightly more than the "buying" price but less than a "private sale price"… Sound familiar? Yes, it works just like car sales.

Most camera bodies do NOT hold their value as well as lenses do. Yours is a 5+ year old "red-headed stepchild". The D40 and the D90 are the better, more common choices. If yours is in good shape, you should be able to get $250-$350 for it.

Since I'm in the look out for secondhand dSLR's, I wish prices would go well below $250. Nonetheless, there's always eBay to consult prices with.

The D80 is a fabulous camera; I have mine for almost five years (I think) and it's still churning out great shots.

The sale price, as mentioned above, is entirely dependent on the condition, as well as your local market. To be honest, though, you're not likely to get more than a few hundred dollars for it, and if you're upgrading, it's going to be to a D7000 or D300S. My suggestion would be to keep the D80 around and use it as a secondary/backup camera. It's always handy to have a second body around, in my experience.

I bought someone a used D80 recently as an intro to DSLRs. It cost be about $400 with a lens and some accessories included. This was a craigslist transaction though.

On Ebay it's listed in a range between $500-600 used for the body. Amazon shows $310-800.

Honestly, there's a ton of used D80s on the market, so you'll have to be competitive on price or no one will be interested. Try craigslist, local classifieds, or a camera shop first to see what you can get.