The $250 difference versus all the other costs of building an engine seems like stepping over doughnuts to pick up dog turds, to quote @Rat Bastid
There's no reason a 318 can't perform well except that people self-impose these ridiculous (IMO) budgetary constraints. I don't get it.
There's merit to doing things on the cheap, don't get me wrong, but money well spent is never a bad thing.
Buy the right pistons then self-port your heads, or hit some swap meets instead of ebay to score an intake.