A:AnswerThat would depend on who your phone carrier is and if whether or not they have a special going, at the time I got mine Best Buy had a $250 off iphone 7 and 7 plus and 24 mos at 29.99. So look and see what specials you can find.
A:AnswerWith AT&T, and I am sure this transcends carrier boundaries, once you completely pay for the phone, whether it is an outright purchase or contractually, you own it and can get an unlock code. AT&T has an "unlock my phone" link on their website.