How much cheaper can they get? Most laptops have CPUs/boards with integrated GPUs, and desktop GPUs can be bought for very cheap, as long as you don't buy the latest greatest edition of everything.

It's hard to lose on this one: even an underpowered, integrated GPU will probably do a better job than an average CPU. Desktops have figured this out a while ago, both OSX and Windows have been rendering on the GPU for a very long time and it's not necessarily to enable any extra graphical effects, but just to make the interaction faster, smoother, and more energy-efficient.