I've just posted something on the L&T board about incomes and what they would support: I've put it there, because it's relevant to other novels.

Spoiler alert: The post on L&T contains spoilers for S&S.

For those who don't want to see the spoilers: the Dashwood women have 10,000 pounds between them (1000 for each daughter, and 7000 for their mother). Fanny Dashwood is perfectly right in saying that they will live comfortably, though it is a bad come-down from what they have been used to. They can afford several servants, including a manservant; they would not be able to afford a carriage.