You'd have to compare the difference in price between:
a) JAR CPL/ME (28 hr course CPL course which I believe is 20 hrs SEP and 8 hrs on a MEP)
b) JAR CPL/SE + MEP course (25 hrs SEP commercial course + 6 hrs MEP rating (31 hrs in total))
Of course bear in mind, if you need extra training on the CPL course, additional MEP hours are twice as much as SEP.....
Completely up to you, but in both cases you'll end up with a JAR CPL and MEP rating. If you do the CPL on the SEP you'll also have a single engine on the JAR licence. You won't get the SEP on the JAR CPL if you do the course on the MEP. It'll only have MEP.
VJW