Trader Captains and Merchant Princes (2nd Edition) (1987)

From the introduction:

"Designed for use with STAR TREK: The Role Playing Game, this supplement allows gamemasters to add a whole new dimension to their campaigns. With it, players may enter the worlds of high finance in the STAR TREK universe and may replace the Star Fleet ethic with the freewheeling life of the independent trader.

Included are rules for judging the player characters' actions as they buy private ships, obtain cargos, and turn a profit. The economic system of the UFP is defined for player and gamemaster alike, including details on the UFP Stock Exchange, price lists for useful goods and equipment, and much more."

A 2-book set

Trader Captains and Merchant Princes
This is the GM guide

Spacelanes: The Magazine of Interstellar Trade
This is the player guide