Voltage source connected to single inifinitely long wire
What you are really getting at is:  "What is the impedance of a wire in free space".  That's simple:  376.73031 ohms (approximately).  

To put it differently, a single wire (no ground wire or shield) of infinite length will appear as a 376-ish ohm load to whatever is driving the signal down that wire.  This assumes that the copper in the wire has a 0 ohm resistance.

Here is the Wikipedial page for Impedance of Free Space.