So why not give him that price in writing? I went through the same thing a while ago. Called several dealerships, they gave prices. I told them I was going to ask around. They immediately offered a lower price on the condition that I took the offer right away. I told them I would consider the lower price if they'd mail it to me AND that I wouldn't even consider a new offer if their first offer was much higher than their competitors.
They all mailed me much lower prices than the best offer they made by phone. I forwarded the best offer to the other dealerships. Most offered slightly lower prices, some said they couldn't match. I went with the original best offer because the difference was marginal and I felt best about it (because their first offer seemed fair as the others didn't go much lower). Which I also told them and they seemed to appreciate. Got friendly and helpful service.
I do hate negotiating, but when it's about a lot of money I feel I have no choice.
Incidently, a little while later, as I was still in a negotiating "rush", I tried to negotiate the price on groceries and it actually worked. I felt like a cheapskate and probably won't do that again, but it really surprised me how this is possible while most people won't even think about it.