This is quite straight forward, but there's a few big unknowns in your project spec: (a) what the 'API' is, (b) whether you want the Arduino & Ethershield supplied or if you're supplying them, & (c) what kind of UI & degree of 'finish' you need for the final product (case / switches / etc, as well as whether DHCP will suffice or you need the ability to specify a static IP & therefore a UI with sufficient key-switches to input that). So this quote is necessarily limited to a few hours of work to get the basic project working, with a basic UI, DHCP & no ability to specify a static IP, but no case & no supply of hardware. See my PM for further details :).