Search this forum for 40-6-151... This same question has come up before, and while I couldn't find that specific number listed (in fact all speeding codes are in the 40-6-180 to 40-6-183 range)... and aside from the response I posted in the other thread, the only thing I can think of is that you were cited in violation of a county or municipal code that is not in the Georgia Codes.
As for your question about the fine amount, there is no specific answer. Here's what I found here:
[url=http://dps.georgia.gov/00/channel_modifieddate/0,2096,5635600_8882754,00.html]georgia.gov - Tickets and Fines[/url]
Fines for traffic citations issued by the Georgia State Patrol are set by the local courts. State Troopers do not set the fines and do not collect traffic fines. For the amount of the fine and information on how to answer the citation, contact the county court listed on the traffic citation.
I would assume the same applies to local law enforcement as well as State Patrol.