How to Turn Your Concept Into a Prototype?

Synced0 asks: "Like a lot of people who post/read on this site, I am a software developer. I have experience developing handheld applications and am quite knowledgeable about the hardware that are in various handheld devices , these days. I have been toying around with the idea of building a device that is based on a handheld platform. I have the basics for what I need such as what OS, and platform I will base it on (motherboard, CPU, storage, display panel, etc). The biggest question in my head is where do I go for the actual design of casing, and who I can get to do the final hardware design. I have never designed hardware before, but now that I have my platform and such, where do I go from here? I have some ideas on what the device should look like, but I have no skills of molding plastics. I have all the pieces working on the desk but am clueless how I progress from this stage.Is it very expensive for someone to take concept into a prototype?"