Winter Emergency Bivy Sack

I am looking for an emergency bivy sack. Not to be used in conjunction with a sleeping bag but solely for emergency use for planned single day climbs. I currently have an Adventure Medical Heatsheets bivy sack but I do not think it will be sufficient for winter climbs. I don't care about bug netting or any frills. I would use this sack most likely in a snow cave in conjunction with a winter Belay Jacket. As with all bivy sacks condensation issues are a worry esp. for the winter for an emergency bivy sack. I don't want to have my emergency gear causing more harm then good.

I was looking at something sub $150 if possible. Lightweight and durability is a must.

Possible Choices:

MontBell Breeze Dry-Tec UL Sleeping Bag Cover- $120 (6.3oz)

Adventure Medical Kits Thermo-Lite 2.0 Bivy- $27.95 (6.9oz)

MSR-E Bivy- $68.95 (9oz)

Black Diamond Winter Bivy- $89.95 (9oz)

REI Minimalist Bivy- $64.93 (15oz)

Marmot Alpinist Bivy- $124 (14oz)

Rab Storm Bivi- $73.74 (17oz)

Integral Designs eVent Micro Bivy- $157 (18.5oz)

Wild Things Half Bag- $110 (29oz)

Suggestions? Advice?

Thank you.