It really depends on what you are looking for in a vanity. If you are looking for something specific, or if you have very particular taste, then it may be cheaper to build your own vanity. However, if you are simply looking for a functional and attractive vanity, then it is probably cheaper to buy one. There are many different styles of vanities available at most home improvement stores, and they can range in price from quite affordable to quite expensive. So, it really just depends on your budget and your preferences.