Reiner Knizia published Swap in his 1990 book Neue Taktikspiele mit Würfeln und Karten. The game involves trading in four commodities, which as a tip of the hat to Catan I've made clay bricks, wood, wool and grain, using art taken from game-icons.net.
You start with one of each commodity and the market starts with double as many of each commodity as there are players (ie two for this solo version).
Prices are randomly set each turn by four dice, placed highest to lowest above the commodities in a fixed order, making clay bricks the most expensive and grain the cheapest.
First sell one or more commodities — but only one of each per turn — to get some credit to then buy other commodities — but again only one of each per turn. No change is given, so only purchases where you pay equal or less are allowed.
Winning involves trading up to have two of each commodity. For the solitaire version, the object is to achieve this in as few turns as possible.