It's not that broken.
However... just use a wand.
5 level magic missile (or negative energy ray) wand is 3,750gp. It's in the rules, you won't have people yelling at you that it's broken, and for the price you stated you could get more than 100 charges, which you would only use if you were trying to be something akin to a magic missile machine gun.
As an added bonus, you could carry a wand in each hand! (Not that you could USE them both in the same round or anything, but if one gets sundered, wah-nah-nah, you've got another wand to get sundered the next round too!)
Oh, but yeah, that fits the item creation guidelines, except for the part where it says "Don't do stuff that goes against what we all know makes sense."
Sadly, we all don't agree on that stuff, so this probably won't fly.
You could probably get a wondrous item that did something like a wand if you paid a lot more it, there are guidelines for this (somewhere,) and I've allowed it in my games before. Something like paying 4x but using the wrong feat nets you a similar item to a wand. Or maybe it was 2x. I dunno.