Dunno if this helps or not, but looking at my booked fares for the year, on US Airways (US) it would cost you approximately $2600 to reach Gold (50,000 miles and *G status) or half that for Silver.

In my case, that would be four PHX-LGW (or PHX-MAN) runs @ 12,000 miles each with a few extra miles depending on routing. Add two quick PHX-LAX flights for $100 each at 1,000 miles and you're done. The PHX-LGW flights clock in at just over $.04CPM, while the LAX would run about $.10CPM.

These would be W or V fare basis - deeply discounted and not upgradeable (but counting for 100% EQM). Again, depending on routing you can squeeze a Q fare out of them (which is upgradeable).

I'm sure there is a theoretical lower minimum for status, but this is an actual example. In fact, US recently had a fluke airfare to STX from MDT that was only $78 each way in F. If you booked 9 of those you would exceed the mileage requirements for Gold and would have spent only $1404 (and all travel would be in F!!!)

Hope this helps!

Sean