The laws and rules which are used by Judges and lawyers are sometimes complicated and it is probably not worth trying to represent yourself. You would need to learn in a short period of time what competent attorneys have spent years learning. Unfortunately if you don't do well in representing yourself you may lose many times over the money you thought you were saving in attorney fees. You may also find the expereience to be quite aggravating. It's the same as trying to repair your own TV or car.
Most lawyers charge by the hour for divorce cases.
If you are charged a set fee there could be problems. If the case requires more work than originally contemplated, the lawyer feels ripped off. If the case settles quickly, the client may feel that the lawyer got too much money for the time that was put in. Sometimes it is difficult for people to understand why lawyers' fees can be so high. Many lawyers do not do a good job of communicating with their clients about the work that they are doing.