A cat scratch post incorporates the same basic idea of a perch which is taking a smaller pierce from a overall cat tree and incorporating by itself. Again, this saves on space and money if you're only looking for something in particular than a whole cat tree.
Pretty much all scratch posts are vertical with a few of them going side-ways and have the same general design. Traditionally the scratching material is made from carpet or sisal rope in most cases and these units feature a simplistic design that isn't meant to take up much space or leave a big footprint. Some scratch posts feature a combination perch on top of them giving you a perch and scratch post all-in-one. Some also have a more rustic design with actual tree wood being one of the posts. Some units are designed side-ways to provide greater stability when in use. Cats tend to knock over unstable scratching posts frequently.
Scratch posts are one of the few things almost ever cat owner purchase. Usually cats will trim their claws on some type of surface they need to scratch on. This is normal behavior and purchasing a scratching post will usually save your furniture from the usual markings cats will eave behind if it's not taken care of immediately. Cats also do this to relieve stress and some scratching posts even have toys that hang for the cat to play with to further promote good health.
Most scratching posts will run usually around $50 to $100 which is a fraction of the cost of a regular high-quality cat tree. In the end you'll save space, money and hassle while getting exactly what you want while your cat gets exactly what he or she wants as well.