Lafuma, a French gear-maker, just re-entered the U.S. market in a big way last year and has some very nicely made stuff. Their One Kilo Extreme Comfort is rated to 36 degrees, costs just $89, and weighs two pounds, two ounces (www.lafumausa.com). So it's very close to your specs. Slumberjack makes an even more affordable bag, the Tour Lite, that's rated to 40 degrees and costs a mere $65. Alas, it weighs two pounds, six ounces.
Of course, you can spend a little more and get a lighter bag. As costlier bags generally use down, they remain the warmth-for-weight champ. My own favorite summer bag is the Marmot Arroyo, which is rated to 30 degrees and weighs only one pound, 14 ounces (www.marmot.com). It packs down to nothing with its high-loft, 800-fill down. Sadly, it costs a steep $259, although keep in mind a down bag will last as long as two or three synthetics. You might also consider Western Mountaineering's MegaLite, which like the Arroyo is rated to 30 degrees (www.westernmountaineering.com). It's costlier at $280, but weighs an astonishingly light one pound, nine ounces.
As for removing some down from your current bag, it ain't worth the trouble. You'd have to cut into each down baffle, remove a certain amount, then sew the thing back up. And you'd save minimal weight, because much of the bag's heft comes from its shell and zipper. Better, really, to just get a new bag for summer camping and keep the Marmot for cooler conditions.
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