as for price diff, no where near 50 quid im afraid. a lot lot less, infact about 20 quid.
I just bought a new front tyre for my GS. Cost was £69 fitting to a loose rim, including new valve and balance. 6 months ago, a new front tyre for my Triumph (120/70ZR17, same size as the Fazer) was £91 fitted to a loose rim and balanced, valve not changed. A front tyre on the GS lasts me 14000 miles. That works out at just under half a pence per mile. Spread over 10000 miles, front tyre costs are £49.30. The front tyre on the Triumph lasts me 10000 miles, which means £91 per 10000 miles.
A rear tyre for the GS lasts me 11000 miles, and the last one cost me £95 fitted to a loose wheel, balanced and new valve. Cost per 10000 miles = £86.36. The last rear tyre for the Triumph (180/55ZR17, same size as the Fazer) cost me £115. They last me 7500. Cost per 10000 miles = £153.
So, tyre cost for the BMW over 10000 miles = £135.66
The Triumph comes in at £244 over 10000 miles. An annual difference of almost £110 just on the tyres alone.
The Sprint ST weighs about the same as a Fazer and is less powerful, so its reasonable to assume the tyre life on the Fazer will be less than the Triumph in my hands.
As for the financial aspect of bike ownership, you were the one who first commented on it when you brought up servicing costs at main BMW dealers. You claimed that a Yamaha would be half as expensive to service than a BMW, but then made a ludicrous cost comparison between a BMW dealer and a backstreet ex racer who you have found to service your Fazer. Hardly a vlaid comparison. Fact is, you can find BMW servicing for a lot cheaper than the main dealers. Steptoe charges in the region of £160 for a 12000 service on the GS, which is half the rate of some of the BMW dealers out there. You can save even more by doing it yourself, which is what I do. Its a simple 1910 design after all.
Bob