From your original post, it sounded like you were open to more than one idea. What did "seal it up" mean? I took it to mean you would consider going so far as to get rid of the door functionality entirely.
I have no idea where to find the type of door you're looking for. It doesn't surprise me that it's expensive.
I hesitate to recommend alternatives, because you seem very set on a specific solution, but what about a framed wall with a normal, heavy well-sealed hinged entry door, presumably which swings into your space? If you hung some drapes inside the existing sliding glass doors, then from outside, there would be no appearance of anything unusual. From inside your room, it would look like a standard egress.