a standard spark plug should last 10-20K KM...those better/performance type should last 30-50KM....
Spark plug is wear and tear part...
Also life span of spark plug depend on your engine condition...if your engine makan engine oil / wrong tuning then your spark plug will wear out faster.
I have a set of 4 oem mazda RX-7 FD rims c/w bridgestone 225/50R16 S-03 tyres (50% tread & originally purchased new) for sale. Good as spare for track days, drifting etc.