I would think oil change on the diesel will run close to $400, whereas the gas would probably still be around $100, but I don't know. (guess I will be finding out, as this is our first DP).
The problem I always have at the service shops is the upsell! It seems just for the wifes car oil change they want to flush everything, choke the filler with a bunch of B&G snake oil products to improve performance, and hand you a $1,200 bill everytime you come in. Its hard to get out of there with a standard oil change and filter anymore. When her last car hit 90,000 miles we had the transmission flushed, and it died within the next 500 miles and was nearly $4K for a transmission. There is a line to draw with preventative maintenance, especially with the products bragging about extended miles between service.