Fees are negotiable but be careful about cut rate attorneys. Whether the attorney charges by the hour or a flat fee, all lawyers take the amount of time which they except a case will take into consideration in setting their fees. An attorney offering to handle your case for a lower fee may plan to limit the time worked on the case to the court appearances and is less likely to be available to discuss your case with you. The fact that this is a first (and hopefully only) offense does not mean that your case will take less time to handle. In fact, an attorney typically spends more time with a first offender explaining how the judicial system works. Finally, I can resist making the analogy to medicine - would you expect a doctor to charge less to set a broken bone because it was the first time you broke a bone? The fees quoted to you sound typical. I charge more to account for my more than thirty years experience.
THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.
Most lawyers charge for the value of their time. (Even if they're charging a flat fee, it's going to based largely on how much time they're going to have to spend on your case.) The retainer you were quoted is probably based on how much time the lawyer thinks your case will need.
The amount of time your case will involve has little to do with whether it's your first offense or your tenth. It has to do with how much work the lawyer will have to do. If the case will probably get resolved quickly, the fee will usually be lower. If the lawyer will have to write motions, appear multiple times in court, and go to trial, the fee will usually be much higher.
The attorney's hourly rate is going to depend on how experienced the attorney is, how good they are, and the local cost of living. An amazing lawyer in Manhattan is going to charge a lot more than a so-so lawyer in the middle of nowhere.
The fee you were quoted sounds fairly low, as a matter of fact. So I would guess that your lawyer figures the case will be resolved quickly. Even so, just getting the case together, preparing for the first court appearance, counseling you and getting your case disposed of could take several hours of the attorney's time.