I'm a "frugal millionaire" with liquid, investible assets of approx 1.2m USD (does not include my home, car, etc.) I saved and invested my way to this after about about 15 years of working. My highest yearly income was approximately 160K while my lowest was around 50K. I drive a 10 year old car (which I bought new, in cash) and my mortgage is fully paid off.
I still go to work everyday (unfortunately.) I'd rather work part time, 2-3 days a week as a contractor/consultant, then work on my own projects the rest of the time.
I often wonder how many others out there are like me... "working millionaires."