The marginal costs of production are near zero effectively. The marginal costs of acquiring and retaining a customer are far from zero for a lot of overvalued enterprise saas companies.
Say we've got this mp4 file that everyone wants. Let's use bittorrent for our digital distribution. So we need to: create a torrent, upload it, and then keep their computer on for a couple more hours? Let's pay $400 for the job. I think it's well within the realm for a clever teenager to do it, or a rando you find off of Upwork or Fiverr, that who knows what they're doing, to finish the first two steps in an hour, so I think that rate is plenty generous. But let's also pay for their Internet connection for the month ($100), and a cheapo laptop to do this work on ($500). This brings our digital distribution costs including the cost of labor, using bittorrent, to be able to make billions of copies to be... $1000?
Even if you pay an engineer to do that job, labor doesn't get residuals, so aren't paid for each copy made, so the cost of labor, whatever it is, is essentially flat. Compared to if you were trying to copy and distribute a physical good, the more copies you make, the higher your costs and $1000 just isn't going to get you far at all.
I'm more interested in what you mean by interest rate though, mind explaining how that fits in here a bit further?
Because what is the point of the whole system? We have one system for two different types of goods. One type is limited in supply because it's physical in nature. The other type isn't really limited in supply because it's digital. Why then should the same kind of money be used to pay for them? How about having two parallel money systems, one of physical goods and one for digital goods. How about for digital goods we eliminate copyright and replace it with a system where we grant every person 864.00 digital dollars (DD) each day, and track what eve check person spends their time watching, then distribute the DDs accordingly. So if I spend 2 hours watching a Disney movie, they get DD 72.00 and they further redistribute those DDs to everyone who played a part in its creation.
Then, the government sets up a system where it will buy DDs for $s, so people will still want to make digital goods, but it becomes a distinct system. This lets us ease into a post-scarcity world - because we absolutely already are there for digital goods - but without having to solve some of the issues that UBI faces.