a FFL is a license to buy firearms for resale, or to buy them from wholesalers or from the maufaturers. i' m assuming that you are a minor, since your dad will help you pay for the gun(if i' m wrong, i' m sorry). he would have to go to the gun shop/store and fill out the paperwork. if you want to buy one online, you have to have a FFL take shipment of the gun. most any gun shop will do this for you for a small fee. the dealer near me, told me to find the gun i wanted, make my deal with the seller, pay for the gun and shipping, then my dealer would give me a copy of his FFL to send to the seller. when the gun comes to my dealer, i would fill out the paperwork at his shop. his charge for the transaction would be about $18 for long guns. you can find a good idea of prices at
www.gunsamerica.com. run a search for bushmaster. i believe the prices for the basic, bottom line model is around $600-$800. you might find a better deal on used. check for gunshows in your area, you should find quite a few dealers with them