IPhone 5s plans with Verizon?

My mom has Verizon but she doesn't use her data so I want to get the iPhone 5s and share data with her. With the unlimited plan for talk, text, and shared data, how much would my bill be a month? And would I have to pay like 20$ a month on top of the bill?

Since there will be two lines (yours and your mother), you would be on a shared plan. Verizon plans charges $40 for each smartphone and $30 each for basic phones. So since you want the iphone 5s that would be a smartphone. If your mother has any android or apple phone that too would be considered a smartphone.

Then you have to choose a data plan to be shared. Here is the cost of the data plan.
$50 per month = 1GB
$60 per month = 2GB
$70 per month = 4GB
$80 per month = 6GB

So you have two smartphones. The cost would be 40+40 = $80
Depending on how much data you use, let say you want to share 2GB of data internet between two lines each month = $60

So the total cost for two lines with unlimited talk, unlimited text and 2GB of shared data internet = 80+60 = $140.00

Total cost each month on your bill would be $140.00 each month before any taxes.

So depending on how much you want to pay your mother, each month the bill is a bit more than $140.00 not including taxes yet. Maybe you can arrange to pay half the bill.