You can get away with good Ziploc freezer bags if you seal it using the water technique.I don't have a flamethrower, but if I sous vide in the pot, I assume, I can just sear it in the cast iron really quickly after I pull it out the bag and pat it dry.
the other thing I don't have is the vacuum seal bags, but I do have the vacuum seal machine, so I need to just order that and I'm good to go.