Page 157: a Rich knight pays £9 to £12 each year, and then: "Superlative knights are the most extravagant and impressive of all, requiring £15 per year or more". I'm assuming that it should read £13 per year for Superlative, or that Rich knight should cost £9 to £14 (so that there is no gap in the sequence).

Superlative £13 is correct.