I've had custom cut sizes ordered in wide enough widths to be suitable from Admiral Steel. They do charge for any shearing of plate but it can save you money if you can nest additional blades. As for the jet cutting prices, I haven't ever priced out a single knife - I've always got a quote per hour and worked with the operator on how much their minimum was. One smaller job came out to $8.80 per knife to cut with waterjet, all costs considered, local operator, on high end stainless tool steel for 2 hours of setup, program and cutting + them using my .dxf file converted from a .jpg profile of the knife, to size, on my own time. The job was overall about $300 at that rate if I remember rightly to make it worth their time to do it and mine to invest in it, less the materials which were considerably more expensive as I think that job was for a few different patterns, 30+ blanks with the varied sheets of steel costing a grand or better.
Some operators will likely be willing to take on much smaller jobs. I haven't been ahead of the game enough to get that particular quote underway, one thing holding me back is the scale of things. $8.80 is roughly 20 minutes of my time and I can rough cut with the 5" grinder with a Norton cutoff wheel, profile clean up on the KMG with the platen at 90 degrees, and drill in much less than 20 minutes. Abrasive costs are very minimal per knife for profiling and as well as any drilling. I'd have to grab a bigger job to reduce the per knife cut of the setup and fixed costs, even things like the half hour to drop off the steel then again to pick it up you've got to figure in.