I'm from the UK, and did the E-2 application myself (having found that it took as much time to explain to a lawyer as to write the application). My initial investment was $100k (enough to start a software business, provably). I have been renewing that visa since 1999, while living in NYC.
Now, however (partly to do with having a 3-year-old), I've moved with my family to Singapore. Visa process took 3 days, and is valid for 12months (and a 12month extension will be very doable, apparently).
One aspect of the Green Card process (which is, I believe, somewhat achievable even starting on a E-2, is that you get caught in the US tax regime semi-permanently. Which is taxation on world-wide income. That would make moving to another country relatively painful (and that's partly why there are so few Americans in Singapore : there's no tax advantage to them).
Happy to answer any questions.