This isn’t easy to do. That’s because every brokerage has a listed margin loan rate (usually tiered rates). And they’re almost all relatively high. But margin loan rates are negotiable, and depending on the size of the account, the longevity of the account, any other relationships with the bank/brokerage, size of the margin loan, etc, those margin loan rates will be lower. I haven’t used margin much (and not at all in recent decades), but I know for a fact that the rates are very negotiable.
Here’s an example -
IKBR has among the lowest quoted margin loan rates, and I know that even they negotiate down from there. Now you won’t be getting margin loan rates between 1% and 2% as they were giving a couple of years ago to good accounts, but you potentially could get rates at or even a little lower than current mortgage rates.