Jane Austen is particular in pointing out how rich women in Regency England are the preferred target of men not only in Pride and Prejudice, but in the majority of her body of work.
While wealth has universally been a preferable attainment to find in a potential life-long partner, Regency England represents a time in history when having money equated not only social distinction but power and respect.
In Regency England, wealthy women came with a dowry at the time of their engagement. This consists on an amount of money that could significantly improve the husband's financial status. Along with the dowry, the rest of a marriage contract would be drawn out which will include the wife's income, what she will get if the husband dies, and a number of other stipulations. The richer the woman is, the higher the dowry, and the better the benefits to be drawn from a marriage. The most significant benefit being that the wife's money, unless otherwise legally preserved to her name, becomes the legal property of her husband: a wealthy woman who marries is no longer a wealthy woman but the wife of a now wealthy man who, if wealthy enough, may rise in social class.
A Regency man who is to marry a woman of ready-money is unquestionably going to benefit. Moreover, a rich woman is more than likely also a fashionable one; the multiple changes of clothing and trousseau that rich women required during Regency years gave them the chance to stand out and make themselves quite unique in the eyes of many. A wealthy, fashionable woman would no doubt be a preferable wife to a "man of the world."
When Wickham became interested in Miss King. It was because of her monetary worth with which he could have paid his debts and which he could have freely wasted.
His behaviour to herself could now have had no tolerable motive; he had either been deceived with regard to her fortune, or had been gratifying his vanity by encouraging the preference which she believed she had most incautiously shewn.
Hence, Miss King is mysteriously shipped off to Liverpool to protect her from Wickham and when it is apparent to him that the fortunes of Miss Mary King were exaggerated, Wickham's change of heart conveniently occurs.
The issue of money is quite evident in Regency society. It is a constant topic in Austen's literature, and it seems to have deeply affected her psyche since she touches upon how money can basically make or break a woman's chances in society, starting with the chance of leading a happy married life.