MP3’s will only start loading when someone cicks on the file.
Videos will depend on how you display them but if it’s a separate link, again that won’t affect your bandwidth until someone clicks.
Even cheap shared hosting will be OK until you start getting a lot of people watching/listening at the exact same time.
Google Drive will likely have bandwidth limits (Dropbox certainly does) – bandwidth costs money to deliver but in practice most people don’t get anywhere close to the limits that are hidden behind “unlimited” claims.
Cross the bandwidth bridge when you’re lucky enough to get to it!