It seems liek I've heard numbers all over the place in terms of "how much" it takes. I think part of it is that non of us are weighing it.
to say 2 courses of sinew is a close to meaningless as you can get because it doesn;t say anythign about how thick the sinew was put on.
Also It's obviously goign to depend on how long and wide the bow is.
I recently did a 58" ERC recurve. It was ~1.75-2" wide at the fades, tapering to very narrow tips. I think I used a total of about 5-6 elk back sinews (not particularly large for elk) and 4-6 good size deer sinews or something along those lines IIRC. That was put down in 2 courses, and when dried it was about 3/32" thick or so .... thats a guess though ... thats only from what I can see where the sight window was cut. I think the limbs may have more like 1/8"-5/32"