Upgrade from 13 Pro to 18 Pro on Go5G Plus 55

Naturally, I was traveling when the iPhones came out. Now that I’m home, it’s time for an upgrade (battery like sucks, camera is also going out). I’m on Go5G Plus 55. I have a 13 Pro or a 14 to trade in. Looks like the current promo only gives me $430 (down from $530 originally?). Looks like Costco is giving $100 shop card if I upgrade there. Obviously no way to say, but what are the chances the trade-in value goes down between now and Black Friday? Thought being to hold out and see if they maybe increase trade-ins for the holidays. Additionally, any tips for potentially selling an old but unopened iPhone 14? (Assuming I trade in the used 13 Pro)