How much does the Iphone 4 cost? - 2

My parents told me they would put me on their plan, if I could pay for the phone I wanted. I'm really looking to get a smartphone, so I'm planning on buying the 8gb Iphone 4, with Verizon. Verizon's website tells me that I can get the phone for free with a two year contract. The monthly bill is an estimated 80$. Since my dad would have three active lines (including me) on his verizon account, does the monthly bill go down? If so, to what? What does the two year contract mean? Are they screwing me over, or is it a good deal? Are there hidden fee's they arent telling me about? As a high school student, I don't make very much money, but I really want this phone, and am going to pay for it on my own. What is the best way to go about this? What will my estimated monthly bill look like? I know there are a lot of questions here, but I just want to make sure I'm getting the best deal I can.

Check the apple site, they will have all prices