Although the figure of $500,000 is quoted you can expect to spend another $50,000 or so in fees commissions and charges.
With a bit of luck you will get a taxable 5% return on your investment of the half million. You can kiss goodbye to the other $50,000 forever. Will you be able to get your half million back ? Maybe eventually, I have heard 7 years quoted as realistic, meanwhile the dollar may nosedive further, and you would get more just on deposit with the bank.
Its an expensive but reasonably sure way (if you pick the right scheme) to get a green card.
The worst thing that can happen is that you invest the money, pay the fees , never get the conditions removed green card and cannot get your invested money back- because it is not a guaranteed investment.
Actually that's pretty bad isn't it?