3 quid for the rotax 912
Yes, but
8 × 3 quid (lasting how long?) or
8 × 50 quid (lasting 2000+ hours)
(comparing 4-cyl engines)
are both insignificant on the scale of aircraft operating costs 
And the aircraft plugs at least have a nice watertight top connection.
REM37BYs are about $30 USD each, or $240 total. That wouldn’t bother me if it wasn’t a roughly 50% increase in price over the last 10 years, which incidentally is about how often I buy a set of aircraft plugs. I buy aircraft oil more often, for substantially less than the price I pay for motorcycle oil.
