Ferry on Border Village. Buy Stonemason, overpay by $4, gain two Border Villages and two $3 cards, for a total of $16 value.
That fulfills the "nothing ever costs $0" new condition but doesn't stick to exactly four cards.
Along the same vein, Ferry on Peddler, then pick up two with Stonemason. They'll be $4 each during the Buy phase, but go up to $6 each afterwards, so you'll total $14.