There are many different felony charges, and the amount that a lawyer charges for one as opposed to another may differ. There are a variety of reasons why different felony offenses may cost different amounts.
First, some types of cases are more complex than others. Some cases require great preparation, thorough legal research, and the allocution of the correct resources. Resources may include the use of private investigators, expert witnesses, subpoenaing of records, etc.
Second, some cases take a lot more time for a lawyer to handle. Sometimes the amount of discovery the lawyer receives is so large that it takes days to review it all. Some cases require preliminary examinations, motions, and evidentiary hearings to challenge the evidence being presented. If the case requires a lot of time the criminal defense lawyer may not have the time or ability to take on new cases.