In my experience of collecting guidebooks for well over a decade (stopped two years ago) anything can happen, and it has more to do with luck and coincidence than ever money, although it goes without saying that in auctions those with the thickest wallets usually get the good stuff.
So my advise is to gently tour the second-hand bookshops and charity stores in your area; you never know what you may come across. Besides, it's not that old. Even if it was the only guide ever published doesn't have to mean it's rare. Some of the rarest things that I had I got for remarkably small amounts and sometimes almost for free; meanwhile I know that I overpaid on a few occasions, especially when I was younger and just starting out.
