Water filters come in a variety of shapes and sizes. They can be complex automated whole-home systems or small pitchers that will fit on your kitchen table. And everything in between, like reverse-osmosis system that fit under sink. It comes without saying that application of these solutions varies a lot, just like the cost.
At this point, you need to clearly formulate your requirements to water filtering system, so that you won't be spending extra on something you don't need, and at the same time, will get a product to fully satisfy your needs.