I think a good way of answering this is quoting the famous first sentence of this great novel, that satirically summarises the position of women in the time of the novel and also points towards the way in which they had very few options:
It is a truth universally acknowledged that a single man in possession of a good fortune must be in want of a wife.
The fact is that for women in the novel, the only real option they have to leave home and to become slightly more independent is to marry. There was no possibility in that time of leaving home by yourself and working. Marriage was how you secured your future. If you think about it, this is one of the reasons why Charlotte Lucas marries such a man as Mr. Collins. The alternative would be to end up as an old spinster who is forced to remain as a companion for her mother and is dependent upon the rest of the family to support her.
You also might like to think about the way in which Lydia is presented after she runs away. What is interesting is that, as the Bennet girls are told many, many times by a number of different people, whilst a man like Wickham can engage in sexual relations outside of wedlock many times, for a woman like Lydia to do something like that has a massive impact not just on her own reputation, but the reputation of her family and the way that they are viewed. The other family members would be "tainted by association."
Lastly, I feel a word needs to be said for poor Mrs. Bennet. As ridiculous as she is, she is also quite a pitiable character, as her desperate desire to marry her daughters off comes from a desire to provide both for herself and for her daughters when Mr. Bennet dies. Although this desire is presented in an incredibly humorous way, let us remember that there was a need to provide for the family due to the law of entailment, which meant that no property could be inherited by a woman.