tis is what I have:
IFERROR(VLOOKUP(B29,Prod_table,2,0)+IF(and(B30<>"",Countif(Sheet2!$E$4:$E$9,b30)=0),VLOOKUP(B29,Prod_table,2,0)*VLOOKUP(B30,extras_table,2,0)/100),if(and(and(B30<>"",Countif(Sheet2!$E$4:$E$9,b30)>0),26,0)
then repeating after the + as you did
You could just highlight in the Countif the range of codes you want to add to 26 - or make another table (that would make it easier to modify) of codes to equal $26
This will make big formula - you might do better creating a macro using Case.