By army green what are you meaning is army green? Did you install a skin that's army green or an army green sticker? or is it the Metal Gear Solid green PSP?
If it's a normal black PSP core model with an army green skin, I believe between $90 - $120 on marketplace sites like Amazon. To be honest I don't believe you can sell it for above $120 - Sony currently dropped the MSRP of the 3000 model to $129.99 for a new one, however they sold out at this price in most places.
For the green model, considering no skins/stickers are installed, I'd imagine at least $120 since it's a "limited edition" model that isn't still in production.