I’ve made a differential encoder adapter board that will plug directly into ODrive. It has a BOM cost of $5.73 each (Digi-Key) + the cost of the board ($1.75 for 3 on OSHPark). MIT Licensed, so feel free to fork it and do whatever you need.
It uses the 5V from ODrive and supplies that to the encoder. Supports A, B, and Z differential inputs.
GitHub Repository: https://github.com/Wetmelon/Differential-Encoder-Adapter
OSHPark Shared Project Page: https://oshpark.com/shared_projects/JfDf458t
BOM on Octopart: https://octopart.com/bom-tool/bUMGyQwH