So many things wrong but most have been discussed---yes paintball uses co2, airsoft uses c02, propane, batteries, spring, etc.
Airsoft travels at much higher velocities than paintball, but it is a much smaller projectile, therefore, the impact is lesser. Same thing goes with if you shoot a .2BB in one gun at 10 feet, although it will be a higher fps, the .25BB will hurt a bit more.
Airsoft does do damage, just because airsoft has higher range and better accuracy, you don't "feel it" as much. Or maybe its just because you played with wallmart toys for 10$.
If you get hit close range, its going to hurt (with airsoft.) Assuming they're good guns, which is what you would play against if you actually went airsofting, and not in your backyard)
It does not cost 500 just for the gun and 1000 plus to make it shooting at 400+. I don't know what you're talking about. As much as I hate clones, JG/Echo1 are getting better and they're already high fps at 150$. If you want a good/more expensive gun, it averages 300$. I don't know where you got the extra 500$ for internals, because you can buy a full tuneup kit for 100$ and thats a COMPLETE upgrade. Or if your gun can handle it, all you need is a 10$ spring to put you up to 400fps (only certain brands can handle it stock, but it will wear down your insides quickly if they're not good).
Airsoft and paintball are two different sports-yes, they have some similarities, but mostly they can't be compared, although the rivalrly is always going to be had.
BE WEARY OF PICTURE.