Buy credits as one-time packs. 1 credit = $0.01. Credits never expire.
$1 per GB per month, from 1 to 20 GB. A separate monthly subscription: change the amount or cancel any time in MANAGE BILLING. Your files are never deleted if it ends, you just can't add more until you're under your free 500 MB or resubscribe.
The exact price shows before you press the button.