Yeah it's a 'how long is a piece of string question' as it depends who does it, what they charge per hour and how much they mark up the oil and filter.
£300 or £100 and everywhere in between.
My local back street garage would do it for around £100 plus VAT. £50 labour and same for the consumables. Maybe a few quid more as the N54 will hold a litre or so more oil than any of mine.