Dropping weight from a 70 pound pack is free. You just start leaving the excess stuff at home.
Dropping weight from a 40 pound pack starts to cost some money. I think I did what most lightweight hikers do — I looked at my pack, shelter, and bag weights, and started spending money to cut them down. This doesn’t have to be a lot of money — it’s possible to make a nice tarp, and even good UL packs aren’t that expensive (compared, say, to a Dana Terraplane). It’s even possible to get a nice 2 pound bag for $150.
But even with 40 pounds, I was still able to make a bunch of cuts for free — leaving home a lot of unnecessary stuff cut many pounds from my pack.
Getting below 20 pounds can be cheap — using homemade gear and leaving even more stuff at home. It can also be expensive, by purchasing featherweight down bags and expensive UL shelters and wildly costly UL packs.
I just dropped two pounds from my pack with a 1.5 pound Western Mountaineering bag. At US$300, it cost $150/pound to drop those two pounds. However, I offset some of the costs by selling two bags for about $150 total, which made my wallet happier <g>. I also saved two pounds with a new pack, an SMD Starlite. But that was a gift.
So my base pack is four pounds lighter, and my feet and knees thank me every setp of the way. It was way worth the cost to me.
Ken B