My neighbour has asked me to build her an 'ultra-comfortable, fast, reliable and light bike for use as a townie, gravel path, rail-trail credit-card tourer'.
I figured I could go rigid 1x10, with a proven (to me) comfortable cockpit and tires and try to hit 18lbs and $2000.
My first cut here is close: 18.5 lbs for $2135 + $270ish shipping
I've seen other builds here with 1200gram heavier (and $300 more expensive) suspension forks coming in with a total weight 300+ grams lighter for about the same price. Which means I am giving up 1500+ grams with my parts choices for cockpit, drivetrain, wheels and tires.
My 'light' starting point was an eBay chinese frame/fork/headset/seatpost, light-bicycle wheelset and RaceFace Turbine cranks. My proven comfortable (to me) choices were Schwalbe Kojak tires, WTB Speed She saddle, Answer 20/20 bars and VP platform pedals.
I think I'm missing about 150g and $50 for a pair of Avid Speed Dial SL levers.