Hmmm good question, I'm thinking 1500-2000 quid but thats just an out of thin air guess, I'll have to have a good think and get back to you, things like tyres you don't replace every year so you'd have to take that cost and divide it by two for example if you were going to do it every other year. Servicing again is not that expensive and is not annual, you get oil, Inspection 1 & 2 which is in a cycle so you'd have to take the average.
The more you have set aside the better though, IMO you can never predic anything, i just paid 1k for a clutch/flywheel replacement, tyres not that long ago at 650, will need an mot next month, so likely there will be something a miss, so thats probably 2k total so far this year.