Mp3 audios enhancement (Long term)

We have around 54 short audios (Mp3) that needs to be clean up. All the audios are phone recording (around 35-55 seconds).
Requirement:
1. Professional sound for this voice audios.
2. No audible hiss, hum or room tone between phrases.
3. Pick sit comfortably at -3 db and overall loudness lands around -16lufs.
4. Voice sounds natural. not over processed, with identical character across every file.
5. Files are named exactly as received and saved in mp4 at the original sample rate
Budget: $15
Deadline: 24 hours