There are a number of ways to search for active warrants for free. Many official city, state, county or federal websites make it possible to search anonymously by name for outstanding warrants.
Another no-cost way to check for outstanding warrants on a person is to call the relevant city, county or state office and ask if there is warrant out for the particular person's arrest. Unlike a web search, this is not an anonymous request and due to phone tracing may cause consequences for the person making the call. Similarly, a person can ask a law enforcement officer to run a warrant check on themselves or another individual.