Interested in building custom mobile hardware

Currently I am more of a software guy, my hardware knowledge is limited to basic consumer off the shelf parts, which is to say, it is very very shallow. I am interested in obtaining a more in-depth knowledge of hardware so I can design my own custom ARM and/or Atom-compatible circuit boards and mobile hardware, small cheap things running a custom OS, probably BSD-based, for a specific purpose.

Let’s say for example I want to build something that at a glance, looks like a Nintendo DS, not for gaming, but maybe as an electronic cookbook that can stand up to the elements in the kitchen, or something else, the application doesn’t really matter at this point. And for a challenge, two touch screens instead of one, but a clamshell design, a directional pad maybe some custom buttons. Is it possible to even source all the parts I would need, and for less than a hundred? If the Raspberry Pi can go for $35, I imagine the cost shouldn’t be utterly prohibitive, but what about just getting my hands on the screen panels? Can you even order something anywhere close to the quality of an iPhone 5 screen right now? If not right now, is the likelihood of it being possible in 3 to 5 years time high or low?

I’d love to learn more about hardware and industrial design, but if it isn’t even possible to do the things I want to do simply for lack of affordable parts, I have other hobbies I could take up instead. Thanks in advance! :-)