Like you, I got used to having my personalized ringtones. Also like you, I don’t want to pay for them. I have a large collections of songs and I don’t want to pay for a snippet of things that I already own.
On Android phones, that I have used for all these years, the process is easy. Find a way to slice the MP3 to the part I want, save it as a new MP3 file, and select it as the ringtone. The slicing took time, since I need to listen to the song multiple times to choose the exact segment.
Then, not completely voluntarily, I switched to iPhone. Not that I am a novice to iOS devices; I had many. I just never used iPhones. The switch over was uneventful. Transferring various data from Android to iPhone was cumbersome yet not technically challenging. iCloud was a necessity.
The ringtones stumped me.
After slicing the MP3 segment to less than 30 seconds, I needed to convert the song to AAC, rename the to M4R, move it out of iTunes (!!), play the file from Finder (by iTunes, which will now know there is a new ringtone), then sync my iPhone. After all that, the ringtone will magically appear from the selection. Oh, I have yet figured out a way to remove the ringtones that I accidentally created.
There is an easy way. I could have hack into the iPhone and drop the sliced MP3 into the tones folder. Oh, you did not think this is easier?