One way to phrase it.
Someone(*) did say that the WXC/BoBs were more expensive than the 'Smoothed Merchant Navies because they were designed first, and they learnt how to make a similar loco, but easier to build in the factory so that the unit cost can be less for the MNs
(*) RMWeb or maybe on the Hornby forums.but was also possibly just a guess...
Also - look at the RRP for Dapol's new N gauge WC/BoB models - £223, cough!