I'd agree with others, that you definitely want to shoot for higher than $1M, simply because of inflation and such.
That being said, over the course of 25 years, I'd say $1M should be pretty attainable. Just looking at my own records, when I was 31, ten years ago, I had about $75K combined (investments, 401k, IRA, savings bonds, checking acct). Now, ten years later, I'm hovering around the $660K mark.
Now, I did get lucky in some instances. Some of that came from selling a condo, where I probably cleared around $75K. And most recently, when the market crashed, I maxed out my HELOC and did a lot of investing while stock and mutual fund prices were low.
And I've done other LBYM methods, such as buying mainly used cars, not eating out alot, having roommates, etc.