I think my gearbox oil and filters need changing is this an expensive job

 

Don't have a Volvo with powershift transmission, but I suspect this would be comparable to my VW CC's DSG transmission which requires an oil and filter change every 40,000 miles. That typically costs in the $500 range at a VW dealer (you need to pull the battery/tray out to access the filter) so I'd expect the Volvo service to be in the 500-700 price range.