The cost would probably be AT LEAST what I posted in your other thread.
ON AVERAGE a miner is taking in about
BTC.2 per block in fees
You will need about 450 blocks to push out 1 million TX so figure the miner to push out 1 million transactions with 0 fee is asking them to give up between 85
BTC to 90
BTC So they would probably charge you at least that much.
Now for the other side, the mempool is full at the moment so that is where I get the .2 per block. If it empties you could possibly get it for 1/10 that much. But it might take a while since as the mempool fills up they would want to send out the transactions with a higher fee.
You would probably be better off paying the 1 sat/vb fee sending them out as regular transactions and being done.
-Dave