The job of negotiation is to get a good deal for all. Price is only one part of that - if you only focus on price bad things happen. too low a price and the supplier goes out of business before you get all the product. Too low a price and your supplier doesn't have enough profit to remain in business for the next time you need something. Too low a price and the supplier won't negotiate with you at all next time you need something.

Of course too high a price has issues as well. It is important to pay attention to price. Sometimes you need to break away from a deal because it will never work out.

Long term the best deals are win-win.