I think he's actually got a decent balance already with the ammo packs. The guys with ammo packs all have drawbacks. Bud's got crappy aim at first, only 75 health, and is an attention whore, but he's cheap. Dexter has more health and better aim, doesn't come with the attention whore drawback, but you can't give him a better weapon. The other guys are all badass but they're all expensive.
Once you really get your economy rolling you can support paying $1000 or more per day in salaries but in the beginning that's a bit of a drain on your finances and you don't really need that much firepower yet. I do still like to pick up Ayden early on despite his high salary. He packs so much power that you're fine just taking low tier mercs for the rest of your team for quite awhile and can still take down the toughest bounties.
The worst I've seen so far is a tier 5 bounty with 2 guys in duraplate, 1 with a plasma gun, 1 with an assault rifle, and 2 more guys in combat armor, 1 with an assault rifle and I think one has a pistol. That group is tough to take down with only rifles. You're pretty much guaranteed to lose some people even if they all have duraplate if you only have rifles.