When it comes to game economy, oWoD has most sense. You have your Resource background. Each dot represents mix of lifestyle and income. It also gives solid estimate of what things you can just buy, what you probably can buy if you save and get creative and what you outright can't buy. Then there is Wealth merit that is kind of safeguard, it means you have enough money safely invested and your Resources can't drop (without very good story reason).
D&D on the other hand, well, I stopped pretending it makes any sense long time ago. And, for some campaigns, i just hand waive it all together, especially if they start at tier 2. I just assume they have enough money for normal expenses. I removes money as a motive. Also, it stops players from taking anything not bolted down and selling it. I had players buy adamantium crowbars so they can pry remove adamantium bolts (which they also took) so they can take statues from palace.