There is a wide price range when it comes to water filters. This depends on technology details, materials, and reliability. Are low-cost reverse osmosis filter systems truly high-quality direct flow systems that do not require a tank and still filter up to 2.3 L/min of pure water? Check whether and how often the membranes (the heart of the system) need to be replaced. Ideally, there are MULTIPLE Filmtec membranes that operate reliably without frequent replacement. Also check how safe and pure the plastic materials are in a low-cost filter system. Here you can find additional aspects to consider before purchasing.
Flow-through filters such as ShowerShield shower filters or lime and bacteria filters like WAV or WaterSavior are more affordable because they use a different technology – but still consist of high-quality materials.