I need to do the same thing for my newly acquired 740... I only have the service key (doors and ignition only) and not the master key which also does the trunk and glove box. I called my local dealer and they said it costs $8.95 for them to figure out how to make the key and then grind me one. I was surprised at this affordability from a dealership! Not sure if this is a Volvo key or an "economy" key though.