I've never heard of anyone making stamps out of stainless steel. Usually tool steel is used. It can be cut in its annealed state and then hardened afterwards. But since you don't have the budget for a machine that can cut stamps with a CNC (just the spindle that's capable of the speed you need will cost more than $1000) I'd suggest looking into a photo-etching process instead: How to Electro-Etch a Solid Metal Plaque