There are 4 factors to balance: cost, weight, warmth, bulk. You will not get a real warm, small, light bag that is inexpensive. Gotta decide what you are willing to compromise on. If you are trying to go that low on price, plan to buy a synthetic, not down, and expect it to be a bit heavy and bulky if you want it to be warm. You might want to check into used stuff, gear exchanges, and factory blems.
Tom
