he was doing a duty by a friend ;-)

“And I am sure,” said Catherine, “I know so little of such things that I cannot judge whether it was cheap or dear.”

“Neither one nor t’other; I might have got it for less, I dare say; but I hate haggling, and poor Freeman wanted cash.”

He does admit that it isn't as cheap as it could be! Even so, I wouldn't be surprised if he had already haggled it down as much as he could. He seems the type to do that and then go away to boast about being generous, just because he couldn't get the price down enough to look as though he'd saved loads of money.