So questions to ponder.... and you don't need to answer here if you choose not to.....

what kind of shape is the Minivan in?   is it wore out, or just you are ready to trade?

have you considered keeping the minivan for a "Go Fer" vehicle - something to run to fields with meals,etc., and just buy a nicer vehicle outright for your wife to drive to town, take kids to events, etc ?

or maybe you are unhappy enough with this vehicle that you just "want to be rid of it" ?

maybe do a little research on Kelly Blue Book.....