[Gurps Fan]

At least in historical Sengoku-period Japan, peasants actually could afford teppo, just like many other weapons. That's why Toyotomi Hideyoshi needed to set up a new weapons control law (1588) to prevent peasants from rebelling!

I think if there were something that made weapons for high-society people expensive, it was solely an issue of decoration. Teppo/tandzutsu for wealthy samurai were often ornamented with engraving; those for rank-and-file soldiers were not. If you are the GM, you can always declare that every gun in your gameworld has +3 Styling (CF +9) option.