personally, I would go for “direct fit” components, rather than having local muffler shop to assemble a “Frankenstein exhaust” from universal parts
you can get a general idea on direct-fit parts here: http://www.rockauto.com/en/catalog/nissan,2007,murano,3.5l+v6,1434436,exhaust+&+emission
labor to put it in will wary from “weekend entertainment project” to “local shop to put it on”