[Wonders]

$50-$70 roughly depending where you go.

[Random]

Pretty good price range, Might leave it a while till it raises a little more.

[Versace]

I'd buy them, I miss my gameboys

[GGovan]

Ask gamestop and so at how much they sell these gameboys, check ebay too.
And like everyone else above said, keep it for some years, just store it in a box, and it might be seriously valuable in a decade or two ^^

[sbatz72]

I would not charge more than 75 pounds for it. It seems like a lot of goods. You should want to get 50 to 75 percent of cost when you sell a pre-owned item.