I'm assuming you have lvl 6 trainer??? But 1.2M for lvl 6 trainer is rather too much...
But anyways, lvl 4 is the most effective because they are really cheap and yet still does a great job, and yea even with lvl 4 trainer your trainee would have gotten around 11 pops or so I'm guessing.
Next time you buy a trainer, maybe you should buy a lvl 5 trainer. Lvl 6 is not really useful unless you have a player who can turn into a monster (but do you have one, so maybe lvl 6 is worth it if you have the money...)