It can be done cheap.
For my first cold weather hang in November (in Acadia National Park), I took a knife to the footbox of a 20 year old synthetic winter bag so I could string my hammock through it. 3 small pebbles, and some clove hitched shock cord allowed me to suspend it nicely. The hood cinch shock cord allowed me to prevent air getting between the bag and the hammock. If you're going to do this, don't cut the footbox in the middle like I initially did, cut it as far from the zipper side as possible. My first night I had some discomfort from my feet being too constrained - too much of that footbox was hanging below my hammock. After some more surgery, the second night was fine.
This bag had previously been relegated to 3 season use in a tent as I don't trust the aged insulation, so it was essentially free. (OK, iirc it cost me UKP51 back in 1992, but think I long ago got that value out of it).
I used it with my 15F down bag and an underpad, and was as snug as a bug in a rug, despite it getting down to 20F overnight. I was mightilty glad that I had my 1L yellow nalgene clipped to my ridgeline at about 4am...
I learned some interesting things about winter hanging. For instance, spectacles get _really_ cold hanging on a ridgeline. And that clothes put between the hammock and UQ don't really stay that much warmer than those outside when they're separated from you by a pad and 15F down bag.