A Batman #1 CGC graded 9.4 just sold for $2.2 million. However the thing I want to point out is the price on the CGC graded 8.5 Captain America #1. It sold for $384,000, a very respectable sum. However , last year, a CGC graded 9.4 Captain America #1 sold for $915,000. Less than one grade level differentiated the 2 books and yet the higher grade comic commanded a premium of 140%. Also, a graded comic will command a value of 2 to 3 times that of a non-graded copy of the same book. Why? Because someone with some authority has evaluated that comic and has a reputation of expertise in the field.
Condition is extremely important when selling comics. If you find a box full of comics in a storage unit, they generally will not have been cared for and will not command the price premiums that you hear comics in some cases selling for. If you run across comics and think they are worth money, here is the grading scale that CGG uses when evaluating comics