Unless you have a long record, jail time is unlikely, but the amount of the fine depends on many factors which cannot be predicted here -- which judge is assigned, the police officer, your driving record, your attitude after you were stopped, how well you can represent yourself in front of the judge, etc.
Only if you are found guilty of a criminal offense. Definitely talk to an attorney, these cases are won at a much higher rate than many other types of traffic offenses.
It is unclear by your question how the officer charged you. If you are charged with reckless driving then you are charged with a class 1 misdemeanor, in which jail time is a possibility, although unlikely. If you were giving a traffic infraction, then there is no possibility of jail and you are looking at a fine, points on your license, and court costs.
I agree with my colleagues that it is very important to know your driving record, whether you were polite and cooperative, what jurisdication this occurred in, and other factors.
I think it would be in your best interest to consult with an attorney in the locality where this occurred so that you can get a better picture of what you are facing as far as penalties and possible defenses you may have.
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