It takes me all of a few seconds to make one in iOS garage band. There are also dozens of ringtone apps that will crop it for you and set it up. Just search in the App Store for “ring tone”.
e.g. Ringtones for Me by Apalon Apps https://itunes.apple.com/us/app/ringtones-for-me/id749106884?mt=8
Ringtones for iPhone! (music) by byss mobile https://itunes.apple.com/us/app/ringtones-for-iphone-music/id380908399?mt=8
Or see the instructions near the bottom of GarageBand for iOS (iPhone, iPod touch): Share GarageBand songs
I’ve never spent a penny on ringtones and never will. Once you’ve made one, it’s simple and quick to make as many as you want from anything in your iTunes library. My current one is a 22s clip from Monty Python’s “The Universe” song.