Stairgate

Perhaps she has to buy a new stairgate, fireguard, or fit in a lamp. This may be a big dip in her purse, but in this financial comparison it is trivial.

There should be a stairgate and the door to the garden should be secured so that children cannot get out unsupervised[…]

At this point you realise that you're also on edge because the kids don't know this house, and the eldest might be sleepwalking and there are no stairgates[…]