Don't know to much about price, though it will be much cheaper than any Amigaone (not really comparable anyways).
As a system I guess you would need the Efika, a hdd or a flashcard, some ddr-ram, something to put it in, and a small (to match the efika) powersupply.Don't remember the site but you get these really nice extremely small psu's somewhere. Not sure if you need anything else..
but anyway what I really wanted to say is that using Efika and Aros really won't make an alternative to Windows Vista if using your computer to everyday-stuff. Aros is a niche os on a hobby-level (for now).