Do they get it for free, seeing as it's kinda like their familiar, or do they have to pay for the extra cost?
Familiars cost 100 gp, you know...
Not item familiars.
They have to pay.
Thanks
Now, what's so bad about the Gun Mage? I've only really glanced over it so far...
It boils down to being a Duskblade who can't Channel without spending two standard actions: cast & shot.
Alternatively, he can convert spells into damage for 1d6/spell level, with a max +3 enhancement to hit on lvl 18.
His max spell level is 6th, limited spells known.
Both abilities can only be used with Rune Bullets, which aren't hard to craft, but can become an issue.
All this coupled with d6, 2 skills/lvl, medium BAB and ony good Reflex save. Don't forget the fact that pistols require a standard action to reload.