Hi,
You could use VLOOKUP. This would allow any number of criteria ranges. You
would need to put this criteria table in an out-of-the-way place. I've chosen
Y1:Z9

Row Y Row Z
0 =$B$2*$C2
50 =$B$2*$C3
100 =$B$2*$C4
200 =$B$2*$C5
300 =$B$2*$C6
400 =$B$2*$C7
500 =$B$2*$C8
600 =$B$2*$C9
700 =$B$2*$C10


You can add to this table as necessary.

Then in A2:
=VLOOKUP($A$1,$Y$1:$Z$9,2)
Note: Values of A1 greater than the last criteria (in this case, 700) will
always return the last criteria (B2*C10)
Change the $Y$1:$Z$9 to match the position of your criteria table.

Regards - Dave.