If they had started saving this money for the 22 years since Jane was born there would have been £8,000-10,000 saved towards doweries and supporting Mrs Bennet as a widow.
IIRC Jane Austen said they didn't save, because they were sure there would be a son who would join with Mr Bennet in breakng the entail (although Mr B and the son would both have to survive until the son was 21 to do that).
the money would have been better spent employing a governess to educate the girls and teach them accomplishments - a governess would only cost around £20-40 per year + board.
Elizabeth said they had all the masters they wanted - that would be visiting masters who taught subjects such as music, French, drawing. Elizabeth and Mary both play the piano, so Jane probably learned too. And they had access to their father's library, of course.
Governesses did come cheap, but a cheap governess might not be very well educated herself, or capable of disciplining Kitty and Lydia. And a well educated governess could get a better post.
I suppose Mr Gardiner would have helped if he could after Mr Bennet's death, but he had his own young children to provide for. The Gardiners might have taken on Jane as a governess, perhaps, so she'd be housed and fed.