why did the sailing trip of jim and hector cost them "a pretty considerable number of weeks ' pocket - money " ?

They had to tip the man who brought them home and pay for their broken sculls.

What between tipping the man who had brought us home, and paying for the broken sculls, and for having been out four hours and a half, it cost us a pretty considerable number of weeks’ pocket-money, that sail. But we learned experience, and they say that is always cheap at any price.