Campaign question

I'm really enjoying the campaign rules, but I want to play Prime Brothers.  My problem is that at 150 starting points, I'd be able to field a Captain (the cheapest hero at 105 points) and a Prime Brother at 45 points.  Not a lot of fun with only two models (IMO of course).  So, how many points do you think the "Hero" ability should cost?  I'm thinking of creating a Sergeant out of a Prime Brother, by giving him the "hero" trait.  So at a base cost of 45, how much would you add?  I'd like to able to field at least 3 characters to start, so I'm guessing anywhere between 5 to 15 points for the "hero" ability.  Thoughts?