A major part of the manufacturing cost is the sensor, large sensors are exponentially more expensive than smaller ones. With today's sensor manufacturing technology a full-frame camera cannot approach the price of an APS-C camera.
Just a little lesson in manufacturing economics. The cost of manufacturing has nothing - repeat - nothing to do with the price that any product sells for in the marketplace.
The price in the market, even as "suggested" by the manufacturer is always based on feedback from the market - thats you and me. The lifecycle of a product is not from the ground up, but from the final concept down. Marketing at a company decides it needs a product with feature set "X" at price point "Y" to compete. This is all based on marketing research, focus groups, informed decisions, and gut level feelings of the marketing department. At that point, they go to manufacturing and say "build us this....(whatever)". There may be some back and forth, especially when new technology will need to be brought in. The back and forth is more or less to determine the scale of the expected propduct - its product life, the number of units, how they can also use technology in other products... that sort of thing. At the end of the day - manufacturing's job is to build marketing's product, and do it at the lowest possible price, so that they make the most money. In a company the size of Canon, manufacturing is a seperate company within a company, with their own bottom line. They sell to marketing, which in turn has its own bottom line... but... always.... the actual "cost" to make anything, has no effect on its sale price. The price is always determined by market conditions. Always.
(the above is the condensed version, proto Readers Digest etc etc)