Your total price will be 340,000,000 beli However, if you already have two revolvers, the price will drop to 140,000,000 bell.
Remember, seastone is expensive and pretty uncommon. But since 140,000,000 is a massive amount of money for us right now, I'd like to suggest that for your first purchase, you'll get 48 bullets instead of 24, meaning the price is half. But for every subsequent purchase, you'll get 12 bullets for 70,000 as Sumaru stated. So it's a one-time deal. And that's only if the big man is cool with it.