Robert, the only question would in fact be shielding, since if electro magnetic interference wasn't present any old thing that looks like a piece of wire will work fine. Impedance or gauge of the wire isn't significant, since essentially zero power is carried, just signal. If the cable in question is in fact totally unshielded(even some of the very thin ones often have light shielding)it may not give you any trouble if you don't have many sources of EMI around and you keep it well away from power cords. A coaxial cable, which is by nature heavily shielded, is usually suggested for a sub cable to avoid interference problems. There's no reason that it should run $25; a 12 foot cable(if that's adequate)is available from sources such as Parts Express for $10-$12.
