I think most water jets can cut through stock that's over an inch thick, and they're well priced for the accuracy (within a few thousands on even the thick cuts). WAY cleaner than plasma cutters. Our manifold plate was cut with water jet and we were super happy with the result.
Also, I've heard stainless is a bit more brittle and conducive to cracking, so mild or tempered might work just as well, especially if you're planning on some sort of coating in the future.