According to the immigration lawyer Yudith Feliz you need US$200,000 if you want to receive Dominican residency via investments. It used to be US$20,000. She also talks about other stuff, all related to immigration.
I read that the idea started when the Bolshevics took over Russia and they required everyone to have a passport and have it on their person whenever they stayed away from home over night or were more than about 50 miles away from home. The plan worked out so well that every other country adopted the passport system. I have always been a bit leery of the story, but it is what I read.