So I'm trying to ball on a budget for the new NCAA football game. Tell me if I'm making a mistake…

We currently have a PS4. Plan to:
Buy a GameStop pro membership
Buy a refurbished ps5 disc console so my son can play his existing games
Trade in his old ps4
Buy second controller

Reason being on the membership to get a lower price on the console, larger trade in value for the ps4, etc

Am I wrong here?

I would try to sell it on the secondary market (like TexAgs Classifieds) first. Should be able to get more money than Gamestop will give you with the pro membership. Gamestop publishes their trade in values on their website. I would check what they will offer, add 40-50%, and you will probably be a lot closer to actual value.