You need a strong clipper that can make its way through the dog’s coat. The cheap ones you find at Aldi/Lidl won’t be powerful enough to groom a whole dog and they only have a really short blade that will scalp the dog. They usually include plastic attachment combs – but the quality is so poor that they won’t be of much use unless you have a tiny dog with a really fine coat.
It’s, therefore, better to buy a proper dog grooming clipper with detachable blades -so that you can change the blade to get different lengths.
You can often find second-hand clippers on advertising sites and in Facebook groups for second-hand grooming equipment. Don’t be afraid to buy a second-hand clipper. They have a long life span.
You don’t need to spend extra on a clipper with several speeds – a one-speed clipper is enough when you only groom one dog once in a while.