Ok I’ll admit realistic is perhaps not the right word in a world where some of the top chefs are armless people with an octopus instead of a head. But still there is something about the price list which bothers me.
First change: More realistic looking prices
So I propose the following change the denomination of everything in the price list to one level lower (gp becomes sp, sp becomes cp). Now the key change: 1GP is now 20SP. This means 1gp=20sp=200cp. This is more like all the different medieval systems without the fiddly 12cp to 1sp.
Some examples:
Long Sword (30gp) = 1gp 10sp
Chainmail Haulberk (55gp) = 2gp 10sp
Cloak Silk (15gp) = 15sp
I use the following notation: 1gp 10sp 0cp -> 1g 10/-, 15sp-> 15/-.
This keeps the original price list but changes how the prices look. All other money in adventures, starting money, rent from holdings etc. Are changed in the same way.
Change 2: Pennies everywhere!
A second change is in how people use money. There are no (or very few) gp lying around And for the most part this is just a concept used for accounting. If Adventurers find money it will almost always be in the form of cp. This means that if they find 3Gp of treasure (a lot under these rules!) then that will be 600cp which they need to carry around. Keeping in mind that each 100 coins counts as an item they’ll start to get loaded up fast!

For transporting large amounts of cash they can find a goldsmith/jeweller who can exchange coins for silver bars worth 10sp each. These can be converted into local currency at another city or town. They can also get letters of promise between merchants but only between cities which are regularly trading and where you really trust the merchants (so perhaps not in Blacksand).