An alternative to highlight values which are not the most frequently occurring within a given code, even if there are more than one:
=B2<>MODE.SNGL(IF($A$2:$A$24=A2,$B$2:$B$24))
While this would need array-entering on a sheet, conditional formatting treats formulae as if they are array-entered.
Another way which would highlight all the prices of a single code if they're not all the same could be:
=AVERAGEIF($A$2:$A$23,A2,$B$2:$B$24)<>B2