I assume there's a really high fixed cost involved in creating a cable installation that's insulated and continuously chilled to liquid nitrogen temperatures, but maybe there's a break even point if the amount of current you're moving is large enough? I mean, if you're comparing with an aluminum or copper cable with a cross section measured in meters, that isn't cheap either.
There might not be a break-even point. Maybe ReBCO tape is just more expensive per amp it can transport than ordinary conductive metals like aluminum. Maybe HVDC lines can be boosted to arbitrarily high voltages such that you never need huge cables in the first place.
Superconductors get VERY exciting VERY quickly if they ever quench, and that is a property of the current and superconductor. You can't carry infinite current.
They may be more efficient, but they come with a whole host of challenges that make them difficult to use over long distances or in uncontrolled environments, which is pretty much what you'll have to deal with for long distance utility level power transfer.
There might not be a break-even point. Maybe ReBCO tape is just more expensive per amp it can transport than ordinary conductive metals like aluminum. Maybe HVDC lines can be boosted to arbitrarily high voltages such that you never need huge cables in the first place.