While perusing the internet I came across this interesting chap:
Digital Caliper Pinouts - Robot Room

The modules he is using are pretty cheap, $8.95 from the US:
Digital Caliper With Data Output Port

I was planning on using either hall effect or inductive proximity sensors wired into an arduino for limit switches so I will have enough ports available to put 3 of these bad boys

Would it be possible to use 3 of these digital caliper modules to provide absolute position feedback on a CNC router at low cost I'm not sure if a cnc machine's rapid movement would prove to violent for calipers to measure accurately to their usual precision, any thoughts?