I've been trying to lighten my load as well without breaking the bank. I started with an insanely bulky 20* generic synthetic sleeping bag that weighs in around 5 lbs. I recently purchased The North Face Cat's Meow (20* synthetic) for $150 and it only weighs 2 lbs 13 oz (women's long). That is a huge bulk/weight savings. (I also bought a TNF Aleutian 3S bag for my daughter for about $90 that weighs about 3 1/2 lbs. Not bad considering the cheap price tag). It seems that there are some fairly cheap options out there that can lighten the load some without the high cost of down or top of the line ultralight synthetics. I agree with others to watch the sale forums for great deals on used gear. If I had been patient enough, I probably could have picked up a used Cat's Meow (or maybe something even better) cheaper on the forum.
Good luck and have fun!