You might also check out glass scale sets at Aliexpress. They are a big step above the iGaging and similar stuff, and more like the stuff the big boys use. I bought a 3 axis set for my mill with glass scales and 3 axis decent size readout for under $250. Does the bolt circles and other tricks. The cabling is all protected with stainless steel armor. Pay with a major credit care and the transaction is safe, but takes about 3 weeks for delivery.
Here is an example:
www.aliexpress.com
Here is an example:
112.88US $ 9% OFF|New Complete BIG LCD DRO Kit Set Digital Readout Display with 3 PCS 5U Linear Scales/Encoder/Sensor Length 50mm to 1000mm|dro kit|digital readoutreadout digital linear scale - AliExpress
Smarter Shopping, Better Living! Aliexpress.com
www.aliexpress.com