Are there any?
i would buy one if it was working where you could fire, (with bullet tracers that would collide with objects and terrain) reload, deselect, select.
and you could switch between three weapons.
Oh, also Ironsights.
I could edit the scripts but I do not know how to make them.
I would be willing to pay around 50 USD.
Did you already get Live Demos from Unity3D website?
Please first get this and watching. maybe It can help you make some FPS. ^^
Did you check out the FPS tutorial?
It has just about all of this.
http://unity3d.com/support/resources/tutorials/fpstutorial
There’s a machine gun and a rocket launcher that you can switch between. You could edit the machine gun code and make a rifle or a shotgun easily enough.
You can add a 3rd weapon by just copying the script from the weapon selection for item 1 or 2 and pasting it below for item 3. It works easily, I added a flashlight.
Hope that’ll help you some.