Dissertation
Money is indeed one of the favourite themes of Jane Austen, which provides a satirical social attitude of her time before money, but also raises issues that can create some situations, like the Bennet’ sisters, they are in danger of social decay of their father’s death.
Marriage and money:

Money is a major concern for many of the characters of Pride and Prejudice. The Bennet family is interested in the Bingley family but only for their money. Mrs. Bennet begins to find Darcy nice, long after judge him of unpleasant, when she learns that Elizabeth will marry him, and sees only the material aspects of marriage and the luxury he will get to his daughter "As you will be rich and considered! You'll have so much money, so much jewellery, so crews! Jane's marriage is nothing compared to nothing at all! [...] This is a security ". For her, happiness is achieved only in terms of money.
At that time, the landed gentry is still considered the top of the social ladder. It is therefore not surprising that Lady Catherine de Bourg, so sensitive about the notion of rank, wealth and relationships, hopes to join her daughter and nephew to gather property, and that Charles Bingley, is considering buying land and building a mansion for his complete social emancipation. The cost of the marriage of Wickham and Lydia is detailed: payment of debts, purchase of the task of teaching in the regular army for him, a little money for herself and £ 100 annual charge of Mr Bennet.
Marriage is considered as the only way to be released of parents control, and to stay like an old girl is considered as a negative fate for the girl and the family.
To marry the girls is a strong pressure for the family, even if it is comic, the insistence of Mrs. Bennet to try to force Elizabeth to accept Mr. Collins and his bad temper on the refusal of his marriage proposal shows that well.

Mrs. Bennet is described to be anxious about the future of her five