Sony DPT-S1, first edition, what’s the value?

Hello,
I’m just looking for some information on a subject I’m totally ignorant on, the ereader used marketplace.

I have a first edition Sony DPT-S1 and I’m thinking of selling it. Just a ballpark number, what do you think I could expect to sell it for? It’s in excellent condition. I actually built a metal case for it. What’s a good way to sell it? I can’t imagine Craigslist!

I thinking of a backlit upgrade, like the Mimas or something. Is a upgrade even worth it with the current technology? I’m running a tight budget so don’t have a lot for a new one.

Thanks,
Phil