What are you buying now David
As for costs...pretty much the same as any other 916 type...for a full services (belts/valves/rocker check/fluids etc etc) your looking at £700 + parts from an authorised dealer such as OYB or anything from 25-40 % cheaper from an independent such as AJR or Nelly.
As a side question...are you sure it is an SP3...it will be a 955cc bike if thats the case...I ask as there are not many GENUINE ones around...but there are lots of 916's with extras added.
Be warned...