Fill down changing part, but not all of the formula

How can I get part of the formula to change as I fill down, but some of it not change. See my formula below, I want to fill down, and have the part "'Grecian Order Form'!D8" change to D9, D10, D11, etc as I fill down, but I want the rest of the formula to stay the same, help!

=IF(D8=Prices!B4,Prices!C4,
IF('Grecian Order Form'!D8=Prices!B5,Prices!C5,
IF('Grecian Order Form'!D8=Prices!B6,Prices!C6,
IF('Grecian Order Form'!D8=Prices!B7,Prices!C7,
IF('Grecian Order Form'!D8=Prices!B8,Prices!C8,
IF('Grecian Order Form'!D8=Prices!B9,Prices!C9,
IF('Grecian Order Form'!D8=Prices!B10,Prices!C10,
IF('Grecian Order Form'!D8=Prices!B11,Prices!C11,
IF('Grecian Order Form'!D8=Prices!B12,Prices!C12,
IF('Grecian Order Form'!D8=Prices!B13,Prices!C13,
IF('Grecian Order Form'!D8=Prices!B14,Prices!C14,
IF('Grecian Order Form'!D8=Prices!B15,Prices!C15,
IF('Grecian Order Form'!D8=Prices!B16,Prices!C16,
IF('Grecian Order Form'!D8=Prices!B17,Prices!C17,
IF('Grecian Order Form'!D8=Prices!B18,Prices!C18,
IF('Grecian Order Form'!D8=Prices!B19,Prices!C19,
IF('Grecian Order Form'!D8=Prices!B20,Prices!C20,
IF('Grecian Order Form'!D8=Prices!B21,Prices!C21,
IF('Grecian Order Form'!D8=Prices!B22,Prices!C22,
IF('Grecian Order Form'!D8=Prices!B23,Prices!C23,
IF('Grecian Order Form'!D8=Prices!B24,Prices!C24,
IF('Grecian Order Form'!D8=Prices!B25,Prices!C25,
IF('Grecian Order Form'!D8=Prices!B26,Prices!C26,
IF('Grecian Order Form'!D8=Prices!B27,Prices!C27,
IF('Grecian Order Form'!D8=Prices!B28,Prices!C28,"")))))))))))))))))))))))))

Awesome, only now i am getting "#N/A" for any unmatched value, how can i get it to have "" for an unmatched value?