I agree with what most people here have said. Waterproof is more trouble than it's worth, and expensive on top of that. Synthetic is warm when wet and dries quickly. You can't really beat that. Get a simple synthetic bag for $10-$30. If you have some specific requirement you didn't mention consider, as others have mentioned, a separate bivy sack.
Personally, I keep a couple cheapo bags, two solid wool blankets and two of these (large). Although I spend far to few nights using them.
Therm-a-Rest Compressible Pillow at REI.com