Gaining some perspective on the timber supply issue is a little like trying to figure out the stock market. There are many forces at work, some of them real and others mere hype. Everyone seems to have a different opinion and a scarier prediction. And as in the stock market, prices are affected as much by market psychology as by reality. Yet no matter what's driving the lumber market, it is dealers and ultimately builders who pay. As forest industry analysts have predicted, the costs at the lumberyard are climbing in all parts of the country. • In New England, lumber dealers report that fir plywood, supplied by West Coast mills, is up by roughly $1.30 per sheet over the last