cheapest option is Minelab soft case or similar. If you mean to take on a plane and protect from damage and one's that waterproof - then Pelican 1600 hard case like this:
I have the black Minelab bag. Pretty good quality and lightweight. I have 2 800’s in there along with 2 11” coils on individual CF lowers, a 15” on individual CF lower, and a 6” on individual CF lower.