hilsman,
One possible reason is that the gun was an early Purdey Overunder built on a variation of the E.C.Green patent.These Purdey guns have a deeper and frame and are heavier than the later/present version built on the Woodward Patent.As a result these early Purdey Overunders do not command the high price of the Woodward version.As with all Purdey guns regardless of their design,quality is of the highest standard.

Roy Hebbes