For what it's worth, my main dealer (Hedge End) did an auto fluid change for £120.
I could probably have tackled it myself, but the complexities involved made getting the dealer to do the job a no-brainier for me!
As an aside, a previous car (SL500 Mercedes) had a 'sealed for life' gearbox. What this meant was that after 100,000 miles they generally fell to bits. It was widely known that an ATF change every 50,000 miles (frowned upon by MB!) would see the thing last until the end of time. Any independent specialist would do it, but main dealers around me would not. I quite liked this logic - how on earth can gearbox oil last for 10,15 or even 20 years and still perform well? If I still have my ISF as it approaches 6 figures, ill get the gearbox fluid done again.