Hi J. - I didn't read all the posts, so sorry if this is a repeat :)
The question is more "should" you move than "can" you move. I am the child of 4 divorces. "Luckily", I was only "involved" in 2 of them. We moved a LOT because of them, though, and it was AWFUL!
We lived close to dad for the most part, saw him every weekend, he was involved in all holidays, etc. I was 10 at the time of the divorce, so the situation's a bit different, but the general issues are the same.
You didn't say anything about your relationship with the bio-dad. Is the bio-dad dangerous, mean, evil? If not, has he been a significant part of your son's life? Is the move a "want to" or a "have to" situation?
There's no easy answer, but try to step back and look at the big emotional picture. It may be "easier" in the short run for you, and I know you can't make ALL decisions based on your children. But the big emotional ones have repurcussions that last YEARS, even decades. I barely talk to my mother because her extreme selfishness in her decisions (past and present) were too much to bear.
Do your best not to take the path that looks easy or more convenient - it may not be in the long run.
Good luck and my heart is with you in this tough time.