I've been buying vintage Ladybird books for Z & E for a while now and used to be able to pick them up for pennies. They have definitely got harder to find recently as well as going up in price.
Yesterday though, I found a big bag for sale in a charity shop. Some were scribbled on and missing dust jackets but the illustrations were lovely and Z & E have been enjoying looking at them whilst I take a trip down memory lane.
The best places to find them are charity bookshops such as British Heart Foundation on Whiteladies Road and Oxfam on Cotham Hill. Be prepared to pay anything from 50p up to £3.00 depending on their condition and the shop.