Cold climate sleeping bag recommendations

Hello everyone,

I am a relatively experienced backpacker as I've been doing it since I was a scout decades ago, but I've spent most of my time backpacking in the SE US where it's pretty warm even in shoulder seasons.

I now live in Alaska, and I've quickly found that my sleep system has needed upgrades. I've since upgraded my pad to the Nemo Tensor insulated and had good results, but I'm now looking for something to replace my 20 degree bag that just hasn't quite been enough. In the higher elevations here, it can drop below freezing overnight even in July.

I'm wondering if anyone has any suggestions of sleeping bags that are <4lbs, comfortable down to 0 degrees, and don't cost a small fortune. I'm ok with spending money on good gear, but $800+ for a sleeping bag is not feasable for me.