If that is $300/month is for uncapped 10 gig symmetric, he could serve up to a bit over 3 million gigabytes of data in a month.

That would cost something like $100k in outgoing bandwidth costs if at a cloud service.

The primary way it's better is that many of the distro mirroring services have ways to announce the mirror for specific networks, so people requesting packages in Fort Collins could get them from a local mirror, rather than going across transit.

Well, is running a distro mirror from home better than running none at all? Because that's what it usually comes down too.

I'm already paying for the home connection and not fully utilizing it. I would have to pay more to run it from a colo or cloud.