Probbaly no were less expensive then the kit.

You might try Waytek Wire. They seem to have a fair quantity of specialized products. Note that I have no experience with the company, just know of them. This is not an endorsement, et cetera.

Here is a link that might be useful: Waytek Wire

You may want to Google "trapeze wiring" but it seems to be much more popular in the UK than here in the US, although I do have two sets with lighting fixtures, that I purchased at Home Depot.

As brickeyee alluded to, the kit from Ikea may be much more economical than finding the cable by itself.

searching with
Low Voltage Trapeze Wire OR Lighting
I find :
It can cost about a dollar a foot.
It is common in Australia.
It is indeed the term for the cable used in these exposed situations,
i.e. 12V, stretched taut and carrying a mechanical load.

At Waytek, a selection of wires and cable, including marine wire, UL wire, speaker cables is here:
http://order.waytekwire.com/category2/M50/360/Wire%20And%20Cable/

I'll send them an email asking which cable is the right one for the description above.