This is the yarn I am using for one of the sweaters I am making. To create it, you first spin 2 full bobbins of singles in one direction (S). You then ply them in the opposite direction (Z). Then you ply your 2 bobbins of 2 ply in the original direction (S). There it is, S or Z makes no difference, as long as you alter the direction of spin as I stated. It is pretty simple.
My singles are very fine here. I can spin 5-10' of one-ply this fine in 1 minute. Each bobbin has a little more than 4 oz on it and about 1700 yards. At a rate of 100-200 yards an hour 4 ounces of that one ply takes me 9-17 hours. The plying takes hardly any time, though. Thankfully!
This is the prime reason hand spun yarns are so expensive. They are great to work with if done correctly, but the cost of labor is high. I would charge $10 an hour plus the cost of the fiber (about $3-$4 an ounce). A lot of handspun is bulky weight for this reason as well. Bulky takes less time to spin. I have a difficult time spinning fiber in different diameters than it "wants" to be spun, however. Each type of fiber has different characteristics that call your hands to spin in a different way. The handspun from Kodiak (picutered in the banner) is about 1/3 as fine as this yarn. If I try and spin contrary to what the fiber wants my yarn gets uneaven.