Sounds about right for the dealer. They're at £549 for a cambelt + Water pump change now as well. The last time I got the belt done at VW (2014) it cost £349! The cost of living ever increases.
Mine's at 126K now and the service book is full (£15 for a new one!), so now I don't bother with dealers for servicing or belts. I do them myself. Past 100K FSH is less important, so long as you keep the parts receipts.
Bear in mind the major service can be a biggie, depending on mileage. Spark plugs, fuel filter, cabin filter etc bump up the cost. They are also supposed to give it a full inspection and grease all the hinges etc. Make sure they've done all this if paying that much for a service. Or do it all yourself for a fraction of the cost