If you relax the requirement and go with "Keeping lightweight cheap" then options abound. This is the route I took to outfit my wife and I and our three college-aged children.
It took time, though, perhaps 8 months to outfit all five of us with lightweight gear, and UL in some cases. In the end our base weights were between 12 and 15 pounds. Since then I've replaced a number of items, e.g. some of our 1 1/2" thick 26 oz Thermarest pads have been replaced with 1" thick 13 oz versions.
Ebay was my main source. Used clothing and equipment can go for VERY little, but know your brands and pay attention to the shipping costs
One of the best deals was a name-brand Goretex rain suit (top and bottom) for under $20 (incl shipping). Maybe it weighed 12 oz more than the latest UL wonder, but I didn't care at that point. Clothing that needs minor sewing repairs can be very inexpensive, as can other gear that needs minor repairs.
Another great deal was an UL WM sleeping bag for around $100 (list $250). I think I got an MSR Pocket Rocket stove for under $20. I could go on...
After Ebay, closeouts and similar sales worked well. And I sewed tarps, wind breakers, stuff sacks, etc.
About the only thing we paid list price for was trail shoes. These had to fit well so we just got them from the local mountain shop.