I’ve recorded short stories for librivox.org (the audio equivalent of project Gutenberg) and am currently working on my first recording to be uploaded to audible.com and Amazon. I use a Blue microphones “Yeti” USB mic equipped with a pop filter, and record in a small room where most surfaces are covered to avoid lots of sound reflections.
You’re not going to do this yourself for free, get a good mic and make an effort to prepare your recording space to be as “dry” as possible. I got my Yeti on craigslist for $50 and you can make your own pop filter out of a small needlework hoop for under $5. Not free, but not a fortune.
there is always the option of getting help. get an account on ACX.com and list your book to find a narrator who already has equipment and experience.