Gamestop $50 extra credit bonus is BACK on just ps4 or xbox one, with an extra caveat now: must be traded TOWARDS a ps4 pro or xbox one S
https://www.gamestop.com/trade#!/consoles
The deal runs through 1/21/17, currently PS4 500GB unit trades in at $125 - so $175 total - and xbox one 500GB base unit trades in at $75 - so $125 total, xbox one 1TB trades in at $110 so $160 total.
$175 is the highest you'd get for a launch ps4, even really on ebay/craigslist/etc after fees and stuff, so if you are itching to go from a ps4 to a ps4 pro this is a pretty decent option, especially if you throw in a bunch of games. Going from a xbox one to S isn't as great a deal. They are also not running any great deals like a free game or whatever with a new console purchase, like their christmas deals.
Gamestop does adjust trade values daily so if they get a rush of PS4's in, they could very well drop the trade in value anytime.
If you are in CA or NV there is a 50% game bonus trade going on as well until 1/8/17 (sunday) so you can toss in stuff like FF15, TLG, WD2, etc for $30-40 each. Other states don't have that promo, they instead are running get cash same as credit. Also if you renewed your PUR Pro membership back in Dec during their PUR Pro promo day you will have a 50% trade coupon in your active offers good until 1/21 but only on games NOT consoles, but obviously there is no way to go back and get this coupon anymore.