I would suggest looking for a used MC-20 or MC-30 Nikon release maybe on one of the auction sites or at a local shop. They are well built. An MC-20 saved a D100 with battery grip from a fall off a tripod at a wedding some years ago for me. It was a heavy pull on the connection at the 10-pin plug, but it kept on working. Incidentally, the release plugs into the 10-pin plug on the front of the D700 body-just under the PC terminal.
I would assume that Jessop's or Gray's would probably have some used releases, but not being in the UK, I really can't address that part of your question very well. You might also try the "want to buy" forum on Nikonians. The price of a used MC-20 or MC-30 should certainly be less than the more current electronic cable release, the MC-36/MC-36A. I'm not familiar with the Elinchrom skyport, so I can't help you there.