Update

Further poking suggests for questions (1) Mixed driver on-demand vs worker spot and (2) Both on demand; they both require a custom policy that removes 

azure_attributes.spot_bid_max_price{}

From the definition.

I tried to see if I could then set the spot % to something random like 23

new_cluster:
            apply_policy_default_values: true
            policy_id: ${var.job_compute_policy_id}
            driver_instance_pool_id: ${var.driver_instance_pool_id}
            instance_pool_id: ${var.instance_pool_id}i
            azure_attributes:
              spot_bid_max_price: 23
            autoscale: 
              min_workers: 1
              max_workers: 8
            

This didn't seem to work, including putting spot_bid_max_price inside a curly brace block - at least the job definition in the UI showed azure_attributes as blank.  I assume it defaults to 100.

So outstanding questions are:

1) Setting the spot_bid_max_price for the spot pool

2) Any docs on this scenario.