The cheaper sets are in the family section - where it's just £5 for kids - while it seems to get dearer as you go from the east stand towards the main/south stand. It seems to be a reasonable pricing policy - especially when you remember it cost Saints fans £22 to see Saturday's game at Hamilton!
While Saints have just under 10,000 tickets at present, more will be allocated if the demand is there.
Story source: The Official St. Mirren Website