Answered question
If I don’t choice data in my monthly plan, how much it costs for the data add-ons?
Data add-on
$8.00....500MB
$12.00....1GB
$20.00....2GB
Other answers
It's cheaper for buy it in plan. $1 for 1G. Also you can always remove it and it'll be valid in next billing cycle.
@Ann $1/1gb, must be the beta pricing, now it's $7/1gb, if you set everything to no/zero, it's 8$ base, plus $7/1gb for a total of $15 smallest data plan available.