I got a pair of basic Dunlop safety boots a few months ago, they cost £25 and have steel toe caps, chunky penetration resistant soles and have also proven to be waterproof up to depths of a few inches. They are excellent exploring boots and because they’re cheap I don’t mind them getting covered in all the usual munge, and they can be easily hosed down outside. Only drawbacks are they’re not the most comfortable for walking long distances and clumsy for climbing.