I think a goal that can be affordable, realistic, and enjoyable, is to shoot for a "10-15%" of body weight maximum (gear not including food and water) with 20% tops for a 5-day trek.
Having lectured on the topic of lightweight backpacking around the country, I've seen troops transform their philosophies in less than a year and have their senior scouts hiking 100-milers in five days with total loads of less than 20 pounds.
We use the following guide in our clinics:
http://www.backpackinglight.com/cgi-in/backpackinglight/00068.html'>http://www.backpackinglight.com/cgi-in/backpackinglight/00068.html
and it remains our most popular publication among the Scouting community.
Respectfully,
Ryan Jordan
Publisher, Backpacking Light
The Magazine of Lightweight Hiking and Backcountry Travel
http://www.backpackinglight.com/
Eagle Scout, Troop 360, Burien, WA
Former Hikemaster and Director, Camp Parsons Silver Marmot High Adventure Program (Washington State)