I made most of my gear and ended up with a pretty cheap (if still in progress) setup.
For warmth, I strung up my poncho underneath the hammock, and when really cold I took a poncho liner (blanket/whatever) and used that as an underquilt underneath the poncho. I had my CCF pad underneath me as well.
I unzipped my sleeping bag and used it like a blanket, tucking the edges around me.
As darkhawk424 suggested, I wore my hat to bed, along with a base layer and thermals.
Of course, I got warm and had to adjust some stuff... This was in the mid-30's. Granted, I was sleeping on the back porch (though the house didn't block the wind) so I didn't take weight into consideration too much...