It's for real ... but with a caveat.
I priced an inside cabin on an MSC repo to Cape Town.
Net price on 7ideas : 1306€
Net price on Viva Voyage (UK) : 1714€
The warning concerns "tasas", which are Port Charges/Taxes and which seem significantly higher than the ones quoted for U.S. or UK pax. So there are some awfully low cruise prices on offer, but excluding the "tasas".
Now I quote Viva Voyage as they often sell distressed cruise inventory that the cruise lines don't want to directly dump into the US market, due to low per diems.