SORTED : light-weight rails & screws (ball/trapezoidal)

Before I post off to china, I thought I'd ask here first:-

I'm building a laser-scanner / pre-sensitized PCB exposure unit (old polygon mirror assy from a laser printer, 450nm laser diode, etc). The scanner unit provides the X-axis positioning of the beam, the Y-axis I'll need a sled, that holds the PCB to be exposed. Bed geometry is nothing special, and I'm flexible with size at this time, but I'm thinking no more that 6". Bed is likely 4mm ali-plate, holding nothing more than a few tens of grams of laminate PCB stock. It would be stepped, delayed, laser line-rastered, delayed, rinse-and-repeat, so absolute positioning is fairly important but there would be low dynamic forces.

So... nothing spectacular then.

What I'm after is the hardware to support the build of the Y-Axis - rails (say 12" length), screws, nuts. All light weight, and with the Y-Axis travelling in a single direction without significant opposing forces, then little concern for backlash (so trapezoidal screws would be considered).

Has anyone any light-weight kit lying around that they want to get rid of for cash?

Note: I'm really not after high-end stuff here - if no-one has anything lying around I'll probably just replicate the axis from a RepRap. Or buy chinese 12mm supported rail and trapezoidal screw/nut/stepper.

I think I'm sorted now, thanks to all that read.

I've got two sbr12 + 4 bearings, I think they are around 1200mm long, I've also got a 1605 ballscrew, pre machined and 500mm length with nut.

Send me a pm if your interested, I'm not to fussed about shifting the screw and can probably sort you a decent deal on the rails, I've got a few other bits and bobs to, I've got quite a number of the LM bearings as well (the units inside an SMA) 16, 20mm and I think I've got 12mm as well, could make your own housing and go with bigger unsupported rails maybe ?

.Me