Bear with me here, and feel free to tell me if I am wrong.
If 14 gauge wire isn't available readily (inexpensively) but, say, 18 is, then running the wire twice should yield good results, right?
I am assuming, using smaller wire versus larger:
Multiple runs of smaller wire from the battery to individual loads will increase the voltage drop as opposed to the larger wire.
Multiple runs of smallerwire from the battery to a BUS would be more or less equal to running a single, larger wire. The bus creates an electrically common connection on the far end, basically making your multiple smaller wires the same as a larger wire (the same principle as stranded versus solid)
In the first example, the complete circuit of batt-load-batt on each load guarantees a loss in voltage according to the size of the wire.
In the second example, loads would connect to the bus, therefore drawing power from all of the wires more or less equally.
I ask because it looks like I can run 18 GA wire for much cheaper than 14, and also that I might be being foolish in not using the third wire of the extension cord. After all, 2 runs gets you 6 conductors instead of 4.