I just buy mine on ebay, sometimes you can find them so cheap it is worth trying, but put a SMA coupled/threaded lens assembly on the end of it, of course. Only problem with used cables is if they are burned on the end or not, you could get one that way and polish it clean though, although if melted at all, probably not. Maybe check out ebay sellers who only sell laser stuff and ask. ebay seller Starlight-Photonics might be able to help, he has lots of stuff like that he has not listed and knows what he is selling.
Thanks for the advice. I had a look on ebay. They have the XIRI units on there but want around 200USD for one, I couldn't find any second hand units. I managed to organize one through Alibaba for 87USD plus 40 USD shipping. I think Thorlabs wanted 128 USD for shipping alone.
Just to answer my own question for anyone who may stumble across this thread. The XIRI units seem to be good value. I haven't noticed any heat from the cable and even at threshold levels of power the beam is very intense. I haven't verified the losses against a meter though.