Is waterproof wall cladding cheaper than tiles?

It depends. Waterproof wall panelling is designed to be better than tiles, not cheaper than tiles. Walls need to be thoroughly prepared to take ceramic tiles, and this can be a quite significant cost on top of the installation and purchase costs. Waterproof wall panelling is much more forgiving and will go up over a variety of substrates without any preparation. It is also relatively easy to install so the average DIYer will be able to install wall panelling themselves.