Well, how could be cheaper?. Soil and light in deserts are practically free, and you can build an insulated underground room, live in the same building and go to the work just walking. Not need to spend gasoline moving a ship and also spend electricity in air compressors.
This is agriculture without polinizators; not correct light spectrum; much higher production costs that earth based companies for the same common products in the market; and high probability of losing the harvest. Not telling the investors that thousands of marine organisms will cover any external transparent surface in a few months (blocking all the light if not regularly removed); or that their investment could end just buried by sand; or that the master plan is based in obtaining permits for eight different organisms (and explain them that you need to jump over most current marine laws). It seems that they not even asked a oceanographer what are those thing named 'water masses' and how they move.
Do they want to use copper sulfate for potato fungus? Is super-toxic for marine forms of life. Do they want to use lots of manure? Is not legal to deliberately dump manure in the sea and a risk of faecal bacteria contamination for beaches. Is their plastic fabric covered by tasty green microscopic algae guaranteed against sea urchin's mandibles?.
Bad interest conflicts with local fishermen, algae harvesters, ecologists?. How they plan to deal with this?.
Insurance or private security? This is a high risk activity for the workers. Aquaculture companies need often to hire private security for marine cages (because the risk of thief).
Either they can provide a reasonable anwser to this questions or they are not serious players (or is just a scam).