Considering pretty much all of it is in good condition, It might sell for $70 - $125 - depending on where you are selling it at.
You could get that much If your lucky, but you most likely wouldn't get $125 sadly.
Since there are a lot of new generation systems out - and I think the Gamecube is last generation (I'm not really good with the whole "Generation" stuff, but I'm sure my eight year old brother could correct me if I'm wrong and would also know) - The Gamecube is not worth as much because It is used and I think is last generation.
Sorry If I'm confusing, and please correct me if I'm wrong,
but I basically agree with the first answer - You can get $100 - IF you're lucky...
Good luck with that!!
