Most water/laser cutters have a minimum order (usually around £40 to £50) i’m sure you’re simple little job will fall into that category! If you can provide them with a .dxf file (plenty of free 2d cad packages to make those) then they don’t really even have any set up time. Assuming say you made it out of a sheet of 16gauge ally, the material costs are going to be low too (<£10 easily)
If you don’t mind doing a little bit of hand finishing afterwards (slight deburr etc) then they will charge you evenless (because they can speed up the cutting / use old nozzles)
Google for your closest provider of water jet / laser cutting!