My husband and I are buying a 1970's home from a family member's estate and renovating.

There is a corner fireplace, at a 90-degree angle, not on the diagonal. The opening is two sided at a 90-degree angle. I hope this description makes sense.

The fireplace was evidently converted to a gas fireplace but there are no doors. There are the chain curtains (sorry, I don't know the appropriate term) and otherwise it's just open. As you can imagine, this is very drafty.

I've tried to search for appropriate doors ******, and all I see are custom doors which are quite expensive. I'm not looking for anything particularly decorative and we don't need it as a heat source, we just want to stop the heat loss and occasionally use the fireplace for ambiance.

Any advice?