Im not sure the project makes economic sense even if the power were free.
Typical wholesale contract prices for solar production in the US are on the order of $0.04-0.05/kwh.
If this $17B cable delivers the full 1.75 gigawatts for 12 hours a day for 20 years, the transmission cost alone is $0.055/kwh.
This doesnt even take into account the time value of money, which would radically increase the cost. The line would have to charge $0.30/kwh for transmission to break even with a 5% interest rate. [1]
Plus - if it worked well enough, Singapore might do a major expansion. And sell start selling solar power to their closer neighbors.