Expanding a bit on my comments upthread, which I do find effective IRL negotiating, and combining with Lynn2000 thoughts a bit:
When I am in a negotiation, and there are some deal points (either "must haves" or "must avoids"), which the other side is not agreeing to - or they have deal points I don't agree to - I do take extra care to find out the reasoning of their position. It may not change my position at all, but it is often the case that understanding the "why" for the other side may help me recognize that our considerations are from different aspects of the deal point, which can allow for a "how about doing it this way" rather than "no". As an example - if I was trying to sell a sedan, and the other party insisted on a truck, instead of saying "I can only offer you a sedan" if I ask the reasons for which they prefer a truck to a sedan, and they say they have to move tent poles often, not in bulk but with frequency, I can point out that the back seat of the sedan pushes forward, allowing the sedan trunk to accommodate long tent poles as well as a truck bed.
One thing I think can be very helpful to maintaining a positive tone through a negotiation is to identify, early and repeating as needed, the "shared goal(s)" and whatever key points the parties do agree on. Following on the above sedan/truck example, the shared goal would be "we would each like to close a deal for a vehicle, me selling, you buying". If we both agree the vehicle should be red, get good gas mileage, and have a five year warranty - those are positive agreement points to reference. The rest of the deal is the negotiation, and it helps to keep front and center the points of agreement.
I will say that, generally, final price (or consideration) should be only committed when all other key terms are agreed to, at least in real life, because key terms can change pricing (seven year warranty would add to price more than five year warranty). It is hard to "back off" a lower price offer once it is stated, if the other key terms are not yet fully agreed to in concept between the parties. That does not mean general budget/pricing should not be discussed, just that it should not be "BAFO" (best and final offer) until the deal "scope" and terms are agreed upon.