Map update needed for 2011 a4

Hi all, question, i’m wanting to upgrade my sat nav to allow post code entry and newer maps, audi want £250 to do it, is there cheaper way of doing it? Car is 2011 audi a4 

Have seen few upgrade things on ebay at like £50 but i’m unsure of which one i’d need and weather it will update both?

any advice would be helpful thanks