I don't know the drop rate but I've gotten some good gear running the gauntlet. Let's make a deal is good if you want a guarantee. It's really about time vs money. If you want a specific item right now, go to the blacksmith and buy it. If you want to spend less but still want a certain quality but not a specific item, then use the let's make a deal option. If you don't want to spend anything then keep grinding.