Depending upon which kit you are after, the price varies. If you need the entire kit which covers front, back, centre, safety fifth, strong lines and all parts of the "Y", then that kit is about $379 and replaces everything except the depower line. It's rare that that kit is needed. We sell all of those parts in single packs like front lines only, middle line only, back lines only etc. We have all the parts to suit most bars from North from about 2009.
To my knowledge, no, you can't buy them "cheap" anywhere. Like trying to buy cheap BMW parts from a BMW dealer.
Yeh I just replaced my lines on a 5th bar, except the centre white line below the Y. Unless you ca buy lines in bulk and do your own splicing it's more hassle than it's worth. I looked into it to. Switch lines are similar to norths (old lines from say the 2011 era) but the difference between the front and backs given a high Y, including the fifth that runs all the way up and through the Y to the bar...it's just too much hassle.
I just bought a set and was done with it.
Suppose you you could try and find a second hand bar that has ltitle use...one other option.