Let's Make Better Rpg Currencies

My last setting had regional apocalypse due to the collapse of their Roman Empire equivalent, which resulted in no national currency since the new feudal regime was so incoherent. There were, however, several local currencies that were gaining traction, such as:

• The goblins had a long-standing traditional currency system of specie coins, similar to that in the dnd handbook. However, anyone who wanted to mint currency could. This resulted in what could best be described as a deciduous economy. In the winter, goblin smiths would try to cheat the system by forging random gold, silver, and copper trinkets into coins to buy food with, resulting in rampant inflation. By the time spring rolls around and food starts becoming plentiful again, frustrated goblin smiths begin melting down their near-worthless coins into much more valuable jewelry and trinkets to sell, resulting in a period of rapid deflation until prices stabilize again in the fall. Often the values of the specie coins would inflate and deflate at different rates, resulting in periods where copper coins were more valuable than gold and silver coins but less valuable than bronze coins. Unsurprisingly, non-goblins tended not to bother with goblin currency.
• Most parts of the local Marches ran on a system of favors. I would have kept track of my player's reputations as a sort of credit score, but i decided to ignore this after one player lost his mind at the idea of not being able to buy things with those dolla dolla bills he provably did not have.
• A currency system gaining popularity was formed in a local city, which resembled the British LSD system but where one pound was 360 pence, and the values of the other coins corresponded to the prime factors of 360. Very logical, and I am sure my problem player would have lost his damn mind at having to do actual math to buy things.
• The nobility did not need to bother with currency, and never have. They simply conducted barter in bulk, backed by favors and local prestige. Exchange rates were very stable. As a result, they tended to use whole 5-pound ingots of precious metals as a form of currency when barter would be unnecessarily time-consuming. However, they seemed to see barter as the more civilized form of trade, since you had to actually conduct diplomacy with your fellow nobility to make it happen, so currencies have had to overcome the stigma of being the uncivilized tool of goblins and peasants to become popular. This was, in fact, the main factor behind why a dominant currency had not emerged in the last century.