To begin with, I have this done nearly identical to what your looking for, other than I have pushbuttons on the design for changing the setpoints and its done in a Microchip rather than Atmel processor. Has a 2x8 LCD onboard along with the SHT11. Next, lets get real. For $30? The PCB blank and parts will be at least that much, let alone the engineering for it. True that I have this already done, but I can't just give it away.