I probably misspoke : Put silver in place of gold for every price given in the PHB for a first approach to be more realistic.Actually I totally disagree. The prices, while a bit weird in a few places, make sense overall if you use 1gp is about 50 to 100$.
A pint of beer, 4cp, around 2 to 4 dollars in a bar. Works perfectly.
A warhorse at 300gp which is 30k dollar, a good new car.
Converting that to silver? If you want silver to be worth that much, ok. But strange.
20 gp today is worth about your 30k $ if you asume 1 gp is something like a kruegerand (which i do) so your modern times comparison is not quite correct.
Translated back your 5gp (might be wrong on that but lets assume its 5gp for a dagger) results in your dagger costing 7500 $. I hope you understand what i am trying to point out now.