The bottom end is P (poor) 01, FA (Fair) 2 and AG 3. To answer the question, it really is entirely on you. Depending on the series, price guides may or may not have AG listed. If you figure half the value of a G4 then consider the coin and how it looks to you, then you decide. I have seen some absolutely lovely AG coins. Hell, my 1877 is an AG3 and I feel it is extremely nice for the grade. I paid almost what a G-4 is valued at. To me, it was absolutely worth what I paid.
It depends on you and the coin.