Every OSR system seems to have a different idea of what a gold piece is worth. That's fine, but it does make conversions tricky.
I usually run narrative games. Money is either "trivial" or "substantial" or "a motive with a universal adapter." The exact value of things isn't important, only their relative worth. But in a game where you roll up 2d20 gold piece in a chest, it's nice to have a sense of how much that's actually worth.
The system I'm using for my Goblin Punch-based OSR hack goes like this.
One copper piece is worth about $1. How much is a sandwich worth? About $5. A mug of ale? Well, ale is like bottled water, so $1? $2?
One silver piece is a $10 bill. A gold piece is a $100 bill.
When the rules say "You need 2,000 silver pieces (XP) to reach level 1", what my players will hopefully feel is "You'll need to steal, loot, or earn $20,000 in this tomb to level up." That's a lot of money, but not when you're stealing priceless relics and magic treasures.
How much would you pay for a wand that shoots fireballs? As much as a laptop? As much as car? Probably not as much as a house.
How much would you pay a peasant to dig turnips for an hour? Probably not much. How much would you pay a doctor to reset a broken leg?
It helps players get a feel for the world, and the relative value of things. A chest full of gold coins is like winning the lottery. Replace each one of these dollar bills with a gold coin, and you get a pretty good idea of how much a dragon's hoard is really worth. It breaks down a bit at the high end, but at least now players will get a feel for how much they're being fleeced, or how expensive city life really is.
If historical context is your thing:
The Count d'Armagnac was ransomed for 250,000 francs in 1360 (though as I recall from Froissart he managed to get that number reduced to 190,000 francs). Conveniently, a "franc" in 1360 was almost certainly a livre tournois, or a Tours Pound. There were approximately 20 sois to the franc and 12 deniers to the sous (it's... complicated). Think pounds, shillings, pence.
Anyway, a rabbit cost 5 deniers and a very small chicken cost 6. A mason in the same period (untrained?) made about 40 deniers a week after food and lodging were taken into account.
Given that, my $1 modern dollar to 1cp to 1 denier estimate isn't too bad!