Very nice indeed, scarce combination. I assume you have the AOs for the Efficiency Medal and bars.
I have no idea why MYB does not price subsequent bars. They are more common than the earlier incarnations especially as war service counted as double, so virtually all GV and GVI Efficiency medal holders saw service in WWII, however while single efficiency medal are relatively common on the market and are priced based on the unit, so for example and RA will make £40-50, while a small Yeomanry unit will make a fair bit more, Efficiency Medals with clasps tend not to turn up frequently as singles, they are almost always in groups, which tends to makes sense when you consider that many of the GV and GVI will have seen both First and Second War service. Re MYB the person who does the prices ( a well known dealer north of the Trent) possibly couldn't be bothered.
If you haven't got the AO's for the Efficiency Medal and Bars I can get them for you.
Paul