Earlier quoted context omitted.
They can become a nation where citizens live on boats (if they are ok with that) or on dwellings that exist over water.. or they can increase the height of their island by bringing soil from elsewhere.. or they can make their own islands.
The engineering challenge involved in making that a safe way to live go beyond anything the Tuvaluans can hope to finance.
So, trade could bring wood, materials, solar, desalinaton. If done slowly, over years, as parts submerge, it wouldn't be a massive outlay at once.
I agree.. not cheap, but individual citizens have to buy building materials currently, their new houses would just be on stilts.