The wall units are more for the computer/networking racks where everything is accessed from the front. A studio rack you need to get into the back as easily as the front, so they are usually either frame racks with no sides or the free-standing cabinets.

The frame racks you can get affordably (there are some small desktop racks too - I had a Proel until recently), but the cabs are usually big and expensive.

You could just buy one rail, cut it in two (or even buy two) and with some woodworking get yourself an enclosure at less than half the price?

That is my next stop should I not find something suitable/affordable.