350 sent files per month (regardless of the number of documents).
You start with an enterprise account which is $200.00 per month and includes 10 users and 100 files per month.
Since you have 100 files included, you need to pay for 250 files.
At 250 files you are in the 101-250 files sent per month group @ $175.00, includes another 100 files and the additional remaining files are billed at $1.67 per file.
Calculation of monthly fees
Enterprise account = $ 200.00 (includes 100 files)
Additional 250 files sent: $175.00 + 150 files (250-100) @ $ 1.67 each = $425.50
TOTAL MONTHLY = $625.50