Mícheál,
I bought 2 off 2200 x 25 GSR linear guides for the X axis, 2 off 700 x 20 GSR guides for the Y axis and 2 off 300 x 15 for the Z axis. The THK rep was very helpful and said that customers usually order linear guides that are far too big for the anticipated loads (a comment I have also read somewhere on this site) and he assured me that at the sizes I ordered, they were more than enough to meet my specification of a machine capable of cutting aluminium.
I have always kept an eye on eBay for such components but here, in the UK, eBay carries nowhere near the quantity of useful stuff than the American site and many of them will not ship to UK - besides which shipping costs and possible duties make it difficult to assess the 'real' cost.
At this moment in time, I cannot put my hands on the costs of the rails separately but can let you know if you need that kind of information.
Progress is a little slow at the moment - too much teaching to do
Mike