I won't really blame them tho.... unified currency sounds neat, it is rather ridiculous if time travel is involved tho, i mean it is not a problem using money in the stone age despite minting gold coin there should be difficult
You should, because it's like you're buying everything in cents, and all the forms of currency that comprise dollars including larger denomination bills, don't exist. So, no dime, no nickel, no quarter, no half-dollar, no dollar (bill or coin), no $2, $5, $10, $20, $50, $100, etc. Just "Gold", and everything is in priced in the hundreds of them, so enjoy carrying around giant sacks of heavy currency (if they were zinc coins exactly equivalent to modern American zinc pennies, somehow, then the 300,000G that the orphanage gets from this festival, would be 750,000g, aka 750kg. A night's rest in a modest inn is about 400G, so that would be 1kg; generally you'd want at least a week's worth of rentals, so the cost of just the inn room would be 7kg, under this system).
Prior to currency, the barter system was what was in use; you might trade a bunch of dried meat for milk and fresh meat with the local shepherd, or a table with the local carpenter, or some nails and other misc. bits of metalwork, or maybe some repair work from the local blacksmith. Even further before that, it was primarily the family tribe system, where tribes produced their own goods and shared them internally according to who could best use them, and any trading was done between chiefs of tribes that were on good enough terms with each other; otherwise it was generally murder or enslavement for labour and resources (this was universal).