There are a few ways you could do this, and the Variable power might not be the best way to do it.
The first would be a Summon effect, which would involve buffing a certain number of friendly individuals up to a specific stat block. It'd probably be something along the lines of Summon (Heroic, Multiple Minions X, Horde, Limited to areas with human allies, Self-Powered) (3+2X points per rank).
The second would be a Dynamic Array of effects that boost the stats of people in the area. This might look something like Perception Area Enhanced Fighting (Affects Only Others) (3 points/rank), plus a number of alternate effects for 2 points each. This would let you buff one aspect of every person who can hear you speaking, or to distribute the points between different areas of enhancement up to the maximum. Note that this method would not allow you to bypass the Power Level limits of the campaign - if you're in a PL10 campaign, you might be able to buff PL6 SWAT team officers up to PL 10, but you wouldn't be able to boost the combat stats of other PL10 PCs.
Finally, you could use the Variable power, in which case you did miscalculate its cost: You'd want a Perception Area Variable (Affects Only Others), which would cost 8 points per rank. You wouldn't need the increased range, since it would affect everyone who can hear your voice (unless you're capable of throwing your voice to cause it to appear from a different location), and Split is a flat +1 point, not +1 per rank, but you wouldn't need it since you'd affect everyone in the area equally.
Note that neither of these are limited for a specific duration of 1 minute; this is because the duration of effects in Mutants and Masterminds fall into five categories, none of which are connected to specific times: Instant, Concentration, Sustained, Continuous, and Permanent. In this case, you would want a Sustained Duration, which simply lasts as long as you're able to spend a free action each turn keeping it active.
Also, I'm uncertain what you mean by "grant a free heroic action", but if you mean "Hero Point", then you might be able to model this by giving them ranks in the Luck advantage, up to its limit of 1/2 PL.