There is no investment requirement as such.   The minimum requirement in most cases is that you have a company set up in the US and have an office.  Forming a company is usually very easy to do and can be done online.  You also do not need to spend very much on an office in the US, and so a basic office should be sufficient.  There is no requirement that the business should have started trading as yet.  Another option that many people consider is the E2 Treaty Investor visa category that requires you to show a substantial investment.