I have a minimum order quantity that must be maintained.

Content of cell A1 will vary, B1 will be constant (90) and C1 will be the
resulting cost.

C1 has a minimum order charge of 180 applied to it so:

C1 needs to show 0 when A1 is 0
C1 needs to show 180 when A1 is 1
C1 needs to show variable of A1 x B1 above 180

I hope this is clear.

Many thanks,

Dave