wow, $50 for 300 feet of cable?? dang that's good!
if you are making speaker cable I have used extension cords alot, buy a 50 foot one, cut off the end and solder on 1/4 plugs. Works ok. the cords are bright orange of course....no one will ever "borrow" them
other than that, sorry, but could you say where you found the 300 feet of mic cable for $50?