I am trading my 300ex in tommorow for a 400ex. What do you think that I will get or should take from the dealer? It is in great shape and has a few minor mods.

 

I would try selling it outright first. Most dealers tell you that whatever you have is junk, and not worth much, and they think whatever they have is gold! My favorite line that I get from the dealers when I want to trade in something is "there isn't much demand for these"....LOL They are all the same.