In the past I have actually got some advice from Presa-dad above.
You will have to get your design figured out, then it has to be converted to a print/file that the waterjet can use. Most shops with waterjet cutters will charge based on the estimated time to cut. They base the estimate on the file/print and material being cut. Thicker or harder materials take longer to cut. Waterjet is not the cheapest way to go but probably the best for something that will be front and center. I think most fab shops that have a jet and know stainless would be able to handle it and would say what Presa said, they do it from time to time but signs don't pay the bills. For me, I have a friend who will make prints for me and if I hand him a gun part or something and ask him to reverse Engineer it for me, he will. It helps we are friends and my wife gives him a couple hundred thousand annually in design business.
The weight adds up quick too, so all things being equal, closer to home and having some kind of connection to the shop is better. Talk to Presa_dad. They probably can convert your design to a file but that won't be free either.