You seem to think that contract negotiations, either with staff or suppliers, is a case of telling them how it's going to be and then reaping the rewards. In the real world it just doesn't work like that. It's a balancing act between what you need, what you can afford, and what is attractive to suppliers. If you put out a tender which isn't attractive to suppliers they simply won't bid, they'll find work elsewhere, I can tell you this as a certainty. If you put out a contract a price that's too low, they won't bid, or they'll find the gaps in your contract that allow them to cut corners so they can deliver and still make money instead of making a loss. If you lock down your prices with no yearly increases they'll estimate those increases and front load them into their pricing structures. Suppliers aren't stupid, and they certainly aren't powerless.