The clerk of the court can give you the exact amount. The court's phone number should be on your ticket. You will probably receive a "courtesy notice" in the mail, restating your court date and including the amount of the fine.
Want to save money on your ticket? Go to traffic school. it is less expensive, keeps the points off your record with DMV and could help keep your insurance rates down. Some counties even let you attend over the internet. It is a good deal. Being at 20 mph within the speed limit you should qualify for regular traffic school as long as you haven't gone in the last 18 months in most counties.
If you want to try to pay a lesser fine than the schedule, you could go to court and plead guilty with an explanation. Most Judges will give people a break on the fine when they've taken the time to show up. You can always schedule the case for trial and hope the officer doesn't show up, in that case your ticket will be dismissed entirely. Good luck!