Hemlines in any length are available to choose from. A simple nursing tee will do the trick. Of course, there are unitards and swimsuits that could also be used, but a nursing tee will fit the bill perfectly. This keeps the mother covered while nursing and lets the baby eat at mom's place. There are ways to convert non-nursing clothes to nursing accessible.
Stores have sales from time to time.
Or they can shop where things are always affordable and made to last. It truly depends on where they are looking. I specialize in custom-made garments to fit the mother properly based on their measurements they supply. Pretty much what is seen in standard stores and catalogs can be duplicated into a garment that is nursing-friendly. I've yet to find one that can't be somehow.