In most cases, filters will need to be changed every six to 12 months (but those with very heavy use might need more frequent replacement). Some models have disposable filters, which can run anywhere from $20 to $80 each, on average. If the model has a washable filter, it can last for years with proper care, but replacing it when it does wear out can cost $100 or more. Consider how much it might cost to replace the filter over the long-term and add that to your upfront cost of purchase to determine a more accurate price.