Probably because it depends on length, finish etc. I paid just under £500 for 3m, chrome finish pole. Not cheap but a lot less than Silent Gliss!
I’ve also used motors in the past from Peter Henzell Ebay http://www.ebay.co.uk/usr/phenzell) and have successfully linked Lightwave transmitters in to the remote control on his current generation of motors, although I’ve not physically installed one yet. However, he only sporadically appears on EBay when he has stock!
I have just fitted a Raex curtain pole (http://www.raexmotors.co.uk/) with a LW821 relay and it all works fine! They’re a local firm (to me) and were very helpful, checking that the Lightwave spec would integrate with their motor. They supplied a “blind” RJ11 lead which plugs into their motor and wires into relay.
Now just need to retrofit a control into existing Silent Gliss Metropole tracks!