I noticed that at Cheaper Than Dirt that they have back in stock a GI Gore-Tex bivy sack that is worth much more than the $40 price, especially to wet-climate Pacific Northwest dwellers. (These have a forest pattern camouflage top cover). This is real USGI surplus, made in USA. They are almost-comparable at the 3-letter co-op is well over $200.
I’ve ordered four of these bivy bags, and all were in new or like-new condition. At my slightly chubby 214 pounds and 5′-10″, there is plenty of room. I’d say that anyone under 6′-0″ and 210 pounds should fit inside with a 4 pound sleeping bag just fine. The shell covers bag and head completely adds almost a whole season to the temp range of the sleeping bag you are using, protects you and your bag from the wet, even sleeping directly on wet ground or vegetation. – Karl in Portland