How much will it cost to "upgrade" this material?

While it's sometimes frustrating, the opening line of the response is often "it depends." When a material changes during construction it's important to be clear on the detailing so a well intentioned "upgrade" doesn't become a detractor to the overall scheme of design. This is an example of a stucco wall the client requested be changed to mahogany. Since there were no existing plan details for wood siding, we provided these sketches to the architect for options on corner detailing ranging from lowest labor intensive to most labor intensive.