I'm not OP, but I've looked it up before, and it's actually quite expensive. Ballpark of around $75/night (USD). And, of course, it's slow, so you'll be using a substantial portion of your banked vacation time to do it (if that's a concern for you).
I took a container cruise in 2019 (with this guy [0], do recommend although it's probably not possible in a post-COVID world), and prices for all trans-Atlantic routes I could find were between 150-250 EUR/night. My ship arrived at the starting port 3 days late and at the destination port 1 day late, but the rate was not adjusted. The sole other passenger with me had his destination port canceled, but the company dropped him at a different port and purchased him fare the remaining way on a bus.
