Rubber stamps work well in the right conditions, and sound more affordable for the project you have in mind. They are cheaper than the acrylic soap stamps, particularly if on purchases the custom-make ones. They can be found/purchased flat without being mounted to anything, or mounted to wood (like the one in the video below) or plastic. I have used a variety of flat unmounted rubber stamps with soap and they are fun to use.
Here is a video by Amy Warden of one technique for using rubber stamps to embellish soaps:
To use an unmounted flat rubber stamps in a similar way, place them on the soap surface, then tap lightly with either the side of the hand or a rubber mallet, then remove it carefully. Depending on how soft or hard the bar of soap is, choose an appropriate amount of pressure.
Another useful thing for the unmounted rubber stamps, is that they can be placed inside the bottom of a soap mold facing up and the soap batter is poured directly onto the stamp in the mold. Once the soap is removed from the mold and the stamp removed, the soap is already pre-stamped for you. I've done this several times and you can buy stamps for this purpose usually sold for use with Melt & Pour, but works just fine with CP soap as well.
Afterward, a bit of mica painted on with a tiny paint-brush can create a lovely personalized soap.
ETA: Here is an example of the flat stamps I was talking about. They are call
embossing stamps.