These are one of the better places to get DRO's.
Machine DRO | Digital Readouts | Engineering | Machinery | Digital Calipers
I've heard lots of horror stories about the cheap glass scales. If I was to fit a DRO to my machine I'd use magnetic scales.
A 2 axis setup for my machine would be about £500.
It's hard enough to justify a DRO but when it costs close to the cost of the machine it's a no brainer, I am sure I can live without one of the expensive ones just as well as I can live without a cheaper one.
Peter