I thought down would be expensive too. I got pretty ruthless with myself when I was shopping for a sleeping bag tho. I live in Wisconsin. I hate being cold. There's no way I'd willingly get out of a sleeping bag if it's below 40F outside. And there's no way you'd get me to sleep outside if it was supposed to be below 40F... which tends to start happening in October, and can easily continue til May 31. June, July, August and September usually won't have night time lows below 40F (tho hitting 40F is pretty routine). So I needed a summer weight bag.

Turns out a 35F or higher down mummy bag with a full zipper can be had for under $150, sometimes under $100. I ended up with a REI down Travel Sack, which is $110 at full retail.

If I was the kind of person who actually slept warm, I could probably get away with a silk or polarfleece bag liner. Full zip ones in a mummy shape seem to run about $50. If you're decent at sewing, you could probably cut that by over 50%. In this climate tho... there's no way I could live with just a liner.

A wool blanket comparable to either option would run about $100, minimum, and depending on how big a blanket you need/want, it could easily hit $300. I'd also pitch a fit the moment it dropped below 60F if I just had wool. Wool tends to be warmest when it's in carefully engineered fabrics, and most wool blankets are not designed for warmth.