I wonder what the value of a 1789 1 pfennig coin with a C. on the bottom might be worth.?

Answer 1

Need more information. At that time, 1 pfennig coins were issued by individual city / states. Your coin could be from any one of them. If you can include a photo, I may be able to identify who issued your coin. Frequently, the coat of arms on the coin is the only indication.
With the C mintmark, it could be Prussia.

Added later: I think it might be Saxony (German city - state). If so, it has a crowned coat of arms on the back with a wreath around it. The coat of arms is divided down the middle vertically. The left half is crossed swords and the right half is horizontal stripes. The C mintmark would be Dresden, in this case. Value = $2 to $10, depending on condition.
I still need a photo to be sure.