We pay £20 before midnight and £25 after, even if only a couple of minutes after. We hardly ever need a babysitter as we have 2 older children who often babysit for others who seem to pay about the same. Our DC prefer to babysit elsewhere, if they can, as we only pay £5 for looking after siblings, but also give younger children £2 each if they've been well behaved.
Find out from others what the going rate is in your area, as we once got told off for overpaying
this is not uncommon as my sister also got a telling off when she moved to a new area.