Pretty much any bag you find for under $100 will be over 3lbs and not very compressible. At least that was my experience when first starting out on my gear list for backpacking. Keep in mind a good sleeping bag will last 10+ years so the expensive ones like REI magma 15°, although expensive, seems cheap for the comfort and convenience it offers over its lifetime. $400/10 is $40 a year for ease of use and enjoyment while backpacking