yeah, you can buy one string at a time.. at my local shop, they charge like $1 per string.. I've had to do it a few times when I break my little E string. you'll have to check your local shop and ask if they sell individual strings. if they don't and you do buy 6 new strings, just put on the one that's broken, and keep the other 5 as backups. rather then taking off 5 perfectly good strings.