Dynamic text/button scripting issue

Well, I’m not quite sure how to come about this. I’m making an rpg, and when you want to buy something for 600 dollars, if your money is less than that, I want it so you cant buy it (i.e. go to a differnet frame or display a popup window) …
on (release) {_root.money -= 600;
if (_root.money = "this is where I am confused… how can i say anywhere from 0-599 ) {gotoAndPlay(1);

}

}

so the script just says on release of button, then subract 600 dollars from dynamic text box money, and if money is anywhere from 0 - 599, you can’t purchase it… any ideas? help would be great.