Around $80 for a quite ok one like manfrotto. Get a tall one with 3 sections. Avoid cheapos. Many do not use a head with it, but I find using a head more suitable for me esp in nature shots.
Use it to shoot sports, fast events and some nature shoot. I like it even better when the subject is angled high up on a tree up or low down (river animals, insects, butterflies). It gives me more confidence as my hand is less tired/shaky as well after a long day. My pics come out better with it. You can read up the details in dpreview and other reviews.