To answer your question, of course you would go for the £140 cheaper option but, as always, there is more to it than your question suggested.
The way I would have hoped a previous renter would behave is to make a provisional booking, then (as most people would) shop around and ensure the cost was about right. Then within a couple of weeks come back and confirm or cancel the provisional booking.
The owners gave you, what was probably, several hundreds of pound worth of free accommodation to help you out and you seem to have repaid them by using their trust to hold a provisional booking for over two months.
Life is more than just taking the cheapest option regardless of the ‘cost’ !