Two things.
'Relatively easy in terms of combat difficulty' was a lie.
Second, why is there no price reduction? Think of this. I have human warriors in my militia. Let's say that one man costs 2 gp, since hiring a merc for a day costs 2 sp(in 3.5, can't find in pathfinder), and they aren't mercs, they're defending their homes, yadda yadda yadda.
Now, I can either have a musket and ten bullets issued for a single man. His feats will be, oh, Point Blank Shot, and Run. Run seems strange, but it's a good choice, since it means he can get in range more quickly to ignore armor saves. He will also be issued leather armor and a buckler as some basic, cheap armor that allows him to still run and use his gun. This in total costs about 1627 gp. Exactly that, actually.
Now on the other side, I'll have four men, with heavy repeating crossbows, and two clips of five bolts each. Their feats will be Exotic Weapon Proficiency(Repeating Heavy Crossbow), and either Toughness or Improved Initiative. They'll be issued basic uniforms, as guns blow through armor easily. This costs 1620 gp.
Let's assume, that, for both sides, the Stats block is the following: Str 11, Dex 13, Con 12, Int 8, Wis 10, Cha 9.
The Musketeer now has a total of +2 to hit with his gun(+3 if within 30 ft), which has a 40 ft range, and hits against touch AC within that range, deals 1d12 damage, and has a critical of x4. It also misfires on a 1 or 2, and needs a full round action to reload. I didn't give him rapid reload, because a standard action still means he can only fire every other round.
Lets assume that he's going up against the crossbowmen, with their touch AC of 11, and he's managed to get in range. This means that on average, he'll hit 60% of the time. 10% of the time, he'll misfire, but let's put that aside for now, as it's almost completely chance and will screw up my calculations.
He'll do about 4.355 damage every two rounds in this manner. If he's within forty feet. His effectiveness decreases tremendously if he's outside of it.
Okay? 2.1775 damage a round, average.
The Crossbowmen, meanwhile, have a total of +2 to hit with their weapons, which have a 120 ft range, deal 1d10 damage, crit on a 19-20, and need a full round action to reload every five rounds.
Against the musketeer, who has an AC of 14 total, so they'll hit about 40% of the time. This means about...let's see...8.06(repeating sixes) every round, and that's counting the full round action every five shots.
These people cost the same. The crossbowmen deal nearly four times the damage. They will have more than four times the health. It's your game, true, but if we ever get control of a fortress...my men won't be armed with guns, which misfire. I might have an elite troop of riders, preferably 6th to 7th level people, with rapid shot, rapid reload, and paper(or even better, metal) cartridges, and pepperboxes. This allows them to get off three shots every round. They would be for dealing with heavily armored people that my crossbowmen or longbowmen couldn't.
And remember this. That was with highly expensive repeating crossbows. Let's say I use light crossbows instead, and give my people rapid reload? I now have around 30 people firing every round vs. one musketeer, firing every other round.
tl;dr: Guns are shitty.