Like everything else, the cost of a filter might not be related to the quality or function.
The filter you chose depends on what you are trying to accomplish. There are filtration systems designed to remove sediments, organic molecules, and even iron. Ion exchange filters can remove heavy metals and other ions and replace them with sodium and chloride ions.
I have gotten by without any filtration for 2 years of full time use and many years of extended use of my RV. I only had an issue one time with water full of sediment. I had checked in advance and avoided using that water even though it meant moving on a bit sooner than I had planned.
If you do want to have a filtration system, consider a main filter to remove sediment. I would make sure it does not remove chlorine which would put your water system at risk of bacterial contamination. For drinking water I use a Brita partly because the cartridges are readily available. There are several other final filters that are probably better but it can be difficult to find cartridges while traveling.