More or less how much does it cost in terms of: electricity + hardware devaluation for the stake-pools to mine each ADA?
A fully-saturated pool, minting several dozen blocks per epoch costs the same to run as a pool with minimal pledge and delegation, which may not mint even one block per year.
The assignment of blocks is based on the delegated stake rather than on the processing power of the mining machines, as would be the case in a proof of work system.
It costs me a few hundred dollars per month to run my relays and my producer node, with a backup producer node but this is by no means the cheapest way to do it - some people run them on Raspberry Pis.
If you were minting 200 blocks per month in a fully-saturated pool, and it was costing you $200 per month to run the setup, that's about $1 per block. This block would then be rewarded by the system with a few hundred Ada, which would be distributed proportionally among the pool's delegators.
So, in some sense, you will have "mined" each Ada at a cost of less than a cent each. But, unlike a proof of work system, if you were to scale up the hardware in terms of electricity usage, it would make no difference to the number of Ada that were rewarded to the pool.