yep I got in 1979 at REI for 45 bucks-150 feet of real stiff gold line. William Marler pointed out that they are quite slippery for rappel to begin with but after they fuzz up the rappels slow down. My friends had kernmantle ropes, so it wasn't too embarrasing. We climbed at small limestone cliff in Yellow Springs Ohio called Clifton gorge. You could set up your top-rope, do the climb and then walk up and down the gorge getting rides on other peoples lines-so it was neighborly to set up your own climb for them to share.
in January 1978 at least according to the WC website and corraborated by Mountain magazine because they are not advertised at the end of 1977 in issues 57 and 58 but do appear in a WC ad in the January 1978 issue 59 with a sketch of Ray Jardine on Separate Reality. In that ad #1,#2,#3 can be bought for £22.75 overseas
In the same issue a 9mm by 45m Edelrid goes for £25.50. This price ratio appears to be fairly steady in that 3 comparably sized BD cams cost about as much as 9mm rope in the current mgear catalog. I first saw them being sold out of a pickup truck.