As a former newbee myself, I will spare you the wrath you will most likely receive from others for not doing any searching. First off the first thing I would recommend is to start reading these forums to get an idea of what you want to do. You can spend less then $100 and up to $1000 depending on what you want to do. When searching keep these things in mind:
Screen (VGA, TFT, LCD)
Control (Touch, Touchpad, Mouse)
Power (DC_DC, AC_DC + Inverter)
cASE (Custom or Buy)
Just start reading and you will get a good idea and then ask more specfic questions and people be more then willing to help you out.