The first commercial joystick for the TRS‑80, the STICK-80, was created by Alpha Products (originally Alpha Product Co.). The first advertisement I can find was in the December 1980 issue of 80 Microcomputing. The STICK-80 package included an Atari joystick and interface and originally cost $29.95.
The interface itself was quite simple. An Atari joystick was capable of movement in eight directions. The STICK-80 used the lower four bits of port 0 to map the four main directions (UP, DOWN, LEFT, RIGHT). The FIRE button was mapped to the impossible combination of UP plus DOWN. In-between directions (such as UP plus RIGHT or DOWN plus LEFT) used two bits. This was a very clean design and made joystick support easy to add to games. The December 1980 advertisement stated: “Software authors and distributors: contact us for joystick conversion package for your existing games.” Within a year, almost all TRS‑80 games had joystick support.
By the March 1981 advertisement, the price had increased to $39.95, but the package now included a demo program. Alpha Products also started selling Big Five games along with their joystick. With a purchase of a STICK-80, you could also take 10% off if you ordered two games, or 15% if you ordered three games. As part of the same deal, Alpha Products would also upgrade non-joystick versions of Big Five games for $3 per tape.