I've never bought a brand new white dress shirt and I have multiple in my wardrobe. There are a few things I will never buy new from a store, and a classic white button up is definitely one of those things.
There are so many white shirts to choose from at the thrift store, and if you're lucky you'll even find one with the tags still attached. If you found a second hand white shirt that has seen brighter days, you can soak it in some lemon juice or baking soda to revive it.
A white button up is for sure a staple in your closet, for those days that you just can't find anything to wear - you can throw them on with your favourite jeans and a pair of heels and call it a day.