You want stupid prices. Mercedes want £200 to update the SatNav. For £200 I can buy a new SatNav and quarterly updates for 2 years for that money.
That's nothing. When I leased my last Honda Pilot I asked what the upgrade to the built-in GPS would cost me. "Err.. hang on, let me run the figures" was the response. A minute later he brightly tells me it will be a mere $50 per month on the lease. A quick bit of maths tells me that over 3 years this will cost me $1800. "That's $1800 over the lease" sez me. "Well, if you put it that way" sez the Sales Slime dejectedly. "Bollox" sez I, "I have a cellphone and Google Maps thanks"...