What iPhone? Generally its roughly the refurbished sale price you can get on eBay. But you can always ask direct via Twitter. Of course the value will be for the phone to day and there's no point buying it now. The price will be lower in 6 months time. You should ask then.
And the memory? If you want a price you have to tell us the full story. Regardless, it looks like it buy value is about $600 or so. But obviously that will go down again over the next 6 months as mentioned.