Just wondering if anyone could recommend a decent bag that won't break the bank for an Orizaba attempt in December. I have been looking at the Mountain Hardwear Lamina 0F synthetic bag, Marmot Never Summer 650 down bag (middle expensive), and EB Karakorum 0F Down (most expensive). Any recommendations would be awesome.

Also wondering if anyone could comment on a good layering system: I was thinking of a base dri-fit tshirt, cap3 long underwear top over that, Patagonia R1 hoody over, North Face Leonidas Soft shell, and then a North Face Micro Thunder 800 down light weight puffy to top it all off.

In the hut, the lamina will be more than enough

I used the Rab Ascent 900 -2 bag ($314). Buddy used TNF Superlight 650 0 deg bag ($250 ish). Both down bags and performed very well. Did not use the hut and did not sleep higher than BC.

You may not even need to zip up a bag rated 0f in the hut.

Since you're purchasing a new bag, I'd advise picking something that will work for your future plans, not just for Orizaba.

Thank you all for your input. Greatly appreciated! I got a closeout special on the Never Summer 0F bag. I was considering sleeping a tent outside the hut.

Can anyone provide any advice for the layering system I wrote down? I don't know if I will need a better down parka. The TNF Micro Thunder is warm in conjunction with other layers, but definitely not as big as something like a MHW Nilas or FitzRoy parka. I am not sure if I can get away with layering with the Micro Thunder...maybe even add a puffy 700 fill down vest to the mix. Thanks for any suggestions guys. Highly appreciated.

I'm going there in March and will use a WM Versalite bag, which is 20F.
I'll be sleeping in a tent away from the hut for a very obvious reason.
When I was there in 2011 there was so much noise from totally inconsiderate Mexicans I hardly slept.
The hut was fairly full.
I'm not entirely familiar with your gear so won't comment on it.
I'll tell you what I'm taking and you can draw your own conclusions/comparisons.
S/S Icebreaker merino top, L/S midweight Brubeck thermal top, Wild Things Insulight hooded jacket, MHW Beryllium Pro Shell hard shell.
I took exactly that combination to Pisco in Peru this year and it worked a treat.
One exception this time though, I'll throw in a Patagonia Nano-Air jacket.
I think it's important to make sure your boots and gloves are right.
I was comfortable on Pisco with my Scarpa Phantom 6000s wearing Smartwool Mountaineering socks.
On my hands I had OR PL400s inside Vango Extremities Super Inferno gloves.
I get cold in the hands but that combination worked well.
Lower body I had Icebreaker 260 leggings under MHW Bokta salopettes.