>It would be expensive
It's just Brazilian farmland, I don't see why it will be expensive. It looks like the conservative cost of a productive acre of farmland in Brazil can cost up to 1500 USD an acre, so taking the 2.124 million miles^2 area of the Amazon basin we get a very conservative 2.03T USD to purchase every acre of the Amazon basin at generous upper-end of Brazilian agricultural prices regardless of productivity.
The real problem is... how could you trust Bolsonaro's government or the criminals they've enabled and emboldened to respect your property rights?