Found a 30° mummy bag that is about the same weight as the Kelty Cosmic Down, but half the price: Cabela's Evader 30°. Reviews suggest that it is fairly true to its temperature rating.
Along with the base layers, warm "beanie" hat and wool socks, that should be a nice, comfortable bag, and not really much larger in size than what I carried in the Uintas.
I continue my goal of effective lightweight backpacking without buying really expensive gear. This seems like a good pick; even without sale prices, it's going for about $90 (vs. $170 for the Kelty). If I can find it late in the winter season or in the spring on sale.
If I take my next hike without a stove, I can save almost $100 from my budget of items that need picking up, but I'll need to spend, without question, about $200-250 on some gear improvements, no matter what. This will include new shoes, a new sleeping bag, a new pillow.