Clearly the Bennets are well off, they live in a country house, and have servants and five daughters out in society, which is quite a considerable cost. Compared to most people at the time, they're clearly wealthy. But there's not enough income to bring the daughters out AND save for the future- it's also clear that the Bennets, whilst not in debt, are living at the limit of their income, and it seems like they've been doing so for a while, even before all the daughters were "out".
Realistically, I don't think it's likely Mr Bennet could have saved enough to provide all the daughters with an income indefinitely for their lifetimes, but it's possible that some money could have been put away for each one on their marriage, which would make them more attractive matches.
Marianne Dashwood is essentially a step on from where the Bennet girls are, though- in that her male financial provider has died, and herself and her mother and sisters have been left in straightened circumstances. The economics of Sense and Sensibility don't quite make sense to me- because I think we're supposed to believe that the Dashwoods, on £500 a year, are in really in quite tight financial circumstances, and but for the kindness of Sir John Middleton, they'd be completely stuck.
(In a way, this is what the Bennets are hoping for, I think. Pemberly no doubt has many cottages on the estate where e.g. Mrs Bennet and Mary could live comfortably and rent free)
But later, it seems like Elinor and Edward Ferrars, are going to be able to live comfortably on £850 a year? I'm not sure if it's because Ferrar's role as a vicar comes with a "living", so they won't have to worry about paying rent? Or possibly that £500 is enough to live on, but not enough for the daughters to be "out", which means they have no chance of finding husbands- which then explains why the Bennets are so stretched financially and aren't able to save.
Regardless, I think all these people are actually extremely wealthy by the standards of the time. Without wishing to offend people, it's like people who have family incomes over £100,000 but claim they've got no money because of school fees, etc.