That board has a true eSATA port; running the machine from an eSATA drive on that port should be the same as running it with an internal drive.
But it seems kind of silly. It's a lot more vulnerable to spills and knocks that an internal drive. If you can REALLY get an external eSATA 2GB for less than an internal, just open it up, extract the drive, and install it internally.
But I agree with Paperdoc; that seems backwards, unless someone had a stock of crappy external drives around before the flood.