search & if functions

I am a complete newbie and have had help in creating a spreadsheet to be used as an invoice template. which is attached.

I am now at a point where i am completely stuck, i will try to explain what i need to do if anyone can shed any light on this it will be much appreciated.

I will use row 12 for ease of explanation, it should become clear if you look at the attached file.

=IF(AND(B12>0,C12>0, NOT(ISBLANK(A12))), IF((B12*C12/10^6)<$C$110,$C$110*LOOKUP(A12,$A$75:$A$89,$C$75:$C$89),
(B12*C12/10^6)*LOOKUP(A12,$A$75:$A$89,$C$75:$C$89)),"")

now i want to include a formulae after the ISBLANK statement i think that looks at column A and if the description includes the words 1st m2 and the area is less than 1m2 then it calculates 1 x rate (a75:a89, c75:c89).

Thanks for taking the time to look.