i would assume the over night stay is for you to come round from the anesthetic, and i really would reccomend it if you live 200 miles away.
i was not good after the anesthetic had the op at 10 am, came round at 1pm, and was still drowsy and sicky at 9pm.
im not sure how much it is for the overnight, you would have to call them for a breakdown, but really try and get one as you will need it. either that or find a cheap hotel close by where you can crash for the night and rest
good luck
xx