Packaging a product can make or break a product in more ways than one. In small quantities custom packaging is not cost effective. When quantities are <100, standard enclosures are a good choice. There most likely will be some mechanical alterations necessary (i.e. push buttons, displays, connectors etc.). When quantities grow many enclosure manufacturers offer custom machining and can provide modified standard enclosures ready for final assembly.
Producing a product for the mass market allows the high cost of a custom enclosure to be amortized over a volume that can make it palatable. It's the initial design and mold making costs that generally keep this out of reach for those smaller production runs that must keep costs down.
One way to make your product standout is to put extra effort into the package labeling. This can also become expensive. Many enclosures have recessed areas designated for overlays. Like custom enclosures there are some initial design and screen costs that can be prohibitive for small quantities.