Free: Contests & Raffles.
One fee for all of them. They are just doing a background check on you. Not registering them in your name.
Each FFL determines what they want for a fee for transfers, there is no fee set by the state or the feds it is all up to the dealer. Yes you now have to pay sales tax on the transferred items. Some dealers will give a break on multiple items and some won't. You should check around and find out what your local shops will do. Also 4473 forms are not sent to the feds or the state, they stay at the gun shop for at least five years. All the feds know from the NICS check is that you bought a gun and what kind of gun it is, (long gun, pistol, shot gun) not the exact gun you bought and no serial numbers.