I still own a pair of Air Force surplus tropical weight pants, 50% polyester and 50% wool, bought in the 1980's. They are wonderful hiking pants. The bottoms of the cuffs are pretty raggedy, but the rest of the fabric is in mint condition.

Even 50% cotton gains a lot of weight when it gets wet and is slow to dry, although a lot faster than 100% cotton. I have a pair of name brand nylon exercise pants bought (on sale) at Big 5 Sporting goods for (as I recall) $11. Check for track and exercise pants at the athletic (not outdoor) departments at the big box stores (KMart, Target, WallyWorld, etc.) and the big discount sporting goods chains. Great synthetic (usually some form of polyester) wicking tops and underwear can be found there, too.

As Tom mentions, cotton does have its place--in hot, dry (i.e. desert) conditions you can soak a cotton T-shirt and have your built-in cooler for several hours. In high humidity, though, the cotton just gets soggy with sweat and stays unpleasant.

In cold damp conditions, though, cotton can be a death trap. My daughter got into the early stages of hypothermia wearing jeans with the temp about 60*. We were hiking in waist-high grass and brush which was soaking wet from prior rain. By the time I realized what was going on, she probably would not have been able to save herself. I stopped, set up camp, got her undressed and into two layers of sleeping bag and started forcing hot tea and cocoa into her. At least she learned a lesson about trying to be fashionable on the trail!