</font><font color="blue" class="small">( In a nut shell.........you are not permitted to ground anything with the "neutral conductor" beyond the main disconnect. Hence a 4-wire feed needs to be run to the separate building if you run 220 out there. The neutral and ground cannot be connected together. )</font>
I thought you could run a 3-wire feed to a detatched building (L1, L2, neutral) and establish a local ground under certain situations. This is probably not applicable to him as I think I remember one of the conditions being no other shared utilities (i.e. water) between the two structures. I am pretty sure you are required to establish a local ground on any detatched building whether you run a ground wire or not.
Every time I do the math for running power to an external shed I come up with the same answers. It is pretty cheap to run 1-2 GFI protected 20 amp circuits using direct burial cable. This stuff can be had for under 0.10/ft at the local box store. Anything above that gets a little pricey. Conduit runs .10-.15/ft by itself. Large guage wire can get expensive. The cost difference between running a minimal (1-2 circuits) and installing a 60-100 amp sub is on the order of a couple hundred bucks. Noticable for a weekender project to take power to an existing shed, but not a huge amount if you are spending tens of thousands on a workshop. Certainly less than the cost of bringing a backhoe back to dig a new trench in a couple years when you need more power..
