hi! welcome to the site! so its kinda hard to answer the question without knowing what they include in the service. i assume the valve clearance check is in there and that its self at a dealership will cost you 450$ just kinda depends on what else they include but the valves are the biggest job im sure.
if i were you i would get on a local forum. i found this in your area.
Brissy Riders Club ? Index page
there are probably others as well. a local forum is a great place to meet people in your area and a great place to get the skinny on where everyone takes their machines to be worked on. chances are if you ask on the local forum everyone will point you to the same place. dealerships are expensive. im not saying you wont find good mechanics but you will find better ones at some of the smaller shops. shops ran by old guys who have been turning wrenches for a long time and arent fresh outta uti(motorcycle mechanic school here in the us) these smaller shops offer more personal service and typically charge you less for better work. dealerships are a business centered around making money as the main motivation. understandable, i mean it is a business. however, these smaller shops are often ran by people who are much more involved in the bike community and have other motivation than simply making money. i would become a member of that forum and ask the question; where does everyone take their bikes to be worked on around here? then armed with that info id call and get a second quote for the service. you could probably save some money, get better service, and meet some of your local biking community in the process. if it comes down to it a dealership usually does ok work but expect to pay thru the nose for it.
find out whats included in that service. i can understand your not wanting to dive into doing tha valves but chances are there are things included in that 800$ service that you could easily do yourself and get the satisfaction of knowing its done right and getting to know your bike a bit better.
things like air filter changes n oil changes or coolant flushes are easy jobs you can do yourself and save paying someone 80$ an hour plus the cost of parts to do. these are things anyone with very basic tools and mechanical skills can do. if you ever need sound advice you can always ask here. help is one of the main things this site is all about.