Pricing singles by hand does not scale past a few hundred cards, and a price list that is three weeks old is a price list that is losing you money in both directions.
Set your markup once. Every night, every single you have set to follow the market is repriced from it — converted into your currency, rounded up to the step you choose, and floored so nothing ever goes out at less than you will accept. Anything you priced by hand stays exactly where you put it.