As noted, its mostly related to sensor size. Larger sensors cost a little more, but they also require larger lenses, which cost a lot more. With larger sensors and larger lenses, everything gets bigger, so the idea of a tiny compact camera is also lost, and the price is higher.
A camera with a larger sensor like the G1X costs a lot more, but is still smaller than a DSLR.
Price levels are also greatly related to marketing, it might cost $75 more to make a camera that sells for $500 more. camera manufacturers want to set tiers of prices, and those who want the top tier are the ones who make profits for the manufacturers, while the entry level cameras may be losing money or making just a buck or two each.