Do high-temp vacuum-sealed reusable bags exist?
There are silicone sealable and reusable food storage bags like these that are good for over 400 degrees: Silicone Food Storage Bags Reusable (looks like this particular product isn't currently available at Amazon, but you can find similar items or they may come back into stock; at least it's clear that such products exist).
They are sealed with a channel that slides over the opening.  What comes with it looks like plastic, so you would need to make a similar channel or clip out of metal or some other material that would withstand the high temperature.  You would also need to figure out how to suck out the air and complete the sealing of it.  It might require embedding a tube at one end of the opening, sealing the bag, evacuating it, then sealing the tube.
One other product I can think of that will take the temperature is Reynolds Oven Bags, which works in a 350F oven and comes in various sizes.  Those are designed to be tied with a provided nylon string.  It isn't clear how many uses you would get from a bag, but they're a lot cheaper than the silicone bags.  Again, you would need to find a way to suck out the air and seal it.  You could do something like wrap the opening around a tube, suck out the air, than tightly twist and tie the bag below the tube, perhaps folding the twisted area.
Creating an air-tight evacuation port in a sealable bag can be done, but is often a challenge.  The OP reports a clever idea to solve this.  Sous vide is a cooking method that involves sealing the food in a vacuum bag and cooking it in a water bath at a controlled temperature.  Silicone bags are available for this purpose, and come with an evacuation port built-in.
The OP found these Sous Vide Silicone Bags and reports that they worked.