Eh? "Dowry" is clearly a payment from the bride's family to the groom. If you mean a payment from the groom to the bride's family then that is a "bride price". And frankly I don't see how that is much different from pimping, which is, of course, illegal.
If you do mean that the family are pimping her out then the banker should do some basic calculations - he could have one of the best whores in town for HK$3000 per night or so and he'll probably be too busy to need more than a couple of nights a week. And with that he doesn't need to cover all the other costs of having her on standby 24*365.
Fundamentally, if money is sufficiently important to him that he has to consider the price put on the woman's head (i.e more important than other considerations such as love etc) then he is almost certainly going to be better off just buying by the night as needed.
If, on the other hand, he wants to marry for love then he should just tell the pimps to fuck off, and get married anyway. If the woman doesn't agree to this then she's no different to the whores on Lockhart Road, and so he should simply buy there because it will be far, far cheaper in the long run.