Tapping into the group knowledge - DRO

This is not about Black Boxes or even MDF (interesting treads at
times). I am wanting to come up with a low cost way to build some
quad encoder based scales that don't have wires wrapped around shafts
or other mechanical headaches. Seems to me that using one of the US
Digital linear strips with the HP reader and a sliding mechanism, we
could devise a cost effective device. The problems that plague me
are: What's the best way to build a "trolly" type slider that would
carry the reader. Do I build it into a standard AL extrusion with a
slot milled on the bottom to connect the reader and slide the strip
past with table movement? The DRO kit from Shoot'n Star is reasonable
but the cost of just scales (rack and pinion) seem high.
I would like to be able to build a scale of virtually any length
and maintain accuracy. I have seen most of the links on the build-it-
yourself DRO's and the scale part seems to be the weakest part of the
designs...just my opinions. I think a lot of the guys in the group
would benefit from an easy to reproduce scale for a DRO or for
encoder feedback on any linear motion machine. I would put sets on
my mill, lathe and soon-to-be-started, torch table.
I though perhaps some of the group could do a Vulcan Mind Meld
and come up with some ideas to try. Computers are so cheap now you
can afford to dedicate one to just being a DRO readout.