Well, if you insists that crafting is why you hired me as a wizard, i would simple do the crafting while you guys are out fighting the monsters and still want my share of the treasure (25% if we are a "4"-man party).
Then you can get your items with the full discount (but good luck with that monsters as a effective 3-man party without an arcane caster).
If i travel with you and fight with you i get the full share of the loot regardless of what i do in my downtime.
If i happen to craft some items in my downtime and sell them to you below the listed price you should bloody well be grateful!
And if you start to charge me for every little thing you do in combat, i am total fine with it.
As your employer i am happy to play for your services the amount you can find in the rulebook.
But know that then i will pocket all the treasure we find. Lets see who made the better deal by that...