Found a buyer, thanks!

I have a 3rd generation Kindle keyboard with 3G (this one here) which my husband bought for me for Christmas 2010. I only used it for a couple months before I realized I prefer holding an actual book, so it sat on my shelf for the past 4 years. It also has a nice leather case with a pop out light on it. Amazon trade-in will only give me $3 for it  and I've had multiple bad experiences with selling on eBay lately so I'd rather avoid that. I'm not looking for a ton of money for it; I'd just like to get a reasonable amount that I can use to buy some more books. So, where can I get cash for my old Kindle or is it just too old?

No it's not too old. You might try in the forums on kboards.com or mobileread.com 

You can also try selling it on Amazon, not trading it in, but creating a listing. I have bought and sold some used devices through Amazon.

Maybe someone here will want to buy it!

Look around to see what people are selling them for. I had a Samsung Galaxy Tablet 2 that was a couple of years old and was going to sell in on Ebay after I purchased another tablet. I looked on Ebay and people were only getting between $40 to $50 for them. It wasn't even worth it to list it, because I would have to pay the Ebay and Paypal fees. I ended up taking the tablet to a used bookstore that takes and sells not only books, but DVD's, games and electronics. They gave me $60 in credit. So, it was a lot better to do that.