sound correction on small bits of audio - initial test on 3 files

I have a bunch of 1 min audio files, I need a few seconds of conversation out of each in which I'd like the background noise as muted as possible. I'll need the same thing done over time, probably 50 in all. Also convert from .caf to .mp3 I'd like to do a test on 3 files, they are each about 10 sec long. I need the talking to be clear and the background noise to be cleaned as much as possible. Looking to spend $20 total for this test on 3 files. , I will have many more to come if it goes well.. let me know if you want to do it. All files are up on a google drive..