We read in Ch. 50:

Mrs. Bennet had no turn for economy, and her husband's love of independence had alone prevented their exceeding their income.

Do we think that they could have afforded going to London all the time even if Mr. Bennet had been so inclined? This is all conjecture again, but every person in the world has to make judgments regarding on what to spend money. We can 20-20 hindsight blame Mr. Bennet for not going to London for accessibility to superior teachers and society. We can all play the blame game and decide it was Mr. Bennet's fault... or not. But I think it's more constructive to admire how well Jane Austen created such a realistic character and plot that we can have such passionate debates about his faults!