50,000 is a fairly big service, much like the 100,000. The need to change the water pump, timing belts and whatnot is where the real cost is. $850 (from looking at others) sounds reasonable, but like John and Luca said, ring around and get a quote from all different places.

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Honda Hannspree Edition CBR 600 RR - SOLD
Yamaha FZ1N - Purchased