If you aren't a formulator I would probably stick to store brought. Unless you want to make other cosmetics.
But you really could do something with a few base ingredients that really shouldn't be too expensive. Some cocomidopropyl betaine, decyl glucoside, some BTMS and some hair heaven (mixed extracts), or some Genadvance Hydra, xanthum gum and a preservative. Once you start, you can't seem to stop. Just like Pringles.
As a soaper though you would have oils right?
So you could compromise. at the very least make beard oil. If you don't want to invest in emulsifiers and other raw ingredients.
Buy beard wash or you can make a lye based bar. ♥♥
If you want some help. I have a few basic formulas that can help you start but I would advise to start reading some of the blogs by the fabulous cosmetic formulators & chemists that are interested in sharing their knowledge.