If this isn't the cheapest around (£74.85 if purchased directly from Brooks), then I'd be happy to be proven wrong (mainly because I'll be ordering one within the next few days).
It only appears to be this price for the standard brown and black models - they're asking for an extra £4.97 for the green, mandarin and blue versions (although that's still cheap for the 'rarer' colours).
It's not the lightest saddle in the world, and yes, you CAN pick up a standard seat for a third of the price from your local bike shop - but these Brooks saddles will last for a good few years, and they're so blinkin' comfortable!
You can also pick up the Brooks proofide for £5.47 (RRP of £7.30), if purchased at the same time.
BROOKS - 140 YEARS OF CRAFTSMANSHIP. The undoubted supremacy of Brooks saddles is largely due to their irreproachable quality in every detail. The leather is absolutely the best obtainable and is thoroughly adapted for its purpose. Retention of shape, and even improvement after the break-in period, is the crucial test of a leather top and is one of the chief characteristics of Brooks saddles. A broken-in Brooks is the only saddle whose shape becomes truely yours. An important feature of leather is its porosity. Invisible pores in the hide provide natural ventilation. Brooks saddles are always cool to ride, so they stay comfortable on the longest rides on the warmest days.