I had a couple of Black Mountain Pinnacle Gold Cables which I won at auction on www.audiogon.com.
These are very simply constructed cables and sound very good but don't fool yourself that you would be getting a $900 cable for £70!
Remember BMC are still making a profit on this cable even when selling it for £70, they are a large buyer of Eichmann Bullet Plugs and acquire these for a very good discount against the UK quoted RRP of £70 for four! The Gold/Silver alloy they use in their cables is the same as that used by a number of Cable Companies in the US such as Audio Metalurgy who similarly quote very high RRP's on their website.
Don't be put off by the above, as I said initially these are very good sounding cables and worked very well in my system until I started making my own using the same components as BMC with the exception of using 99.99% silver instead of the alloy, which IMO sounds better.
At retail costs for Eichmann Silver Bullet Plugs you couldn't make a cable as cheap as the £70 they are offering you for a pair so give them a try, I don't think you will be dissappointed!