According to this post[1] they charge based on how long it takes them to retrieve the data. The hourly retrieval rate would be the amount of data you requested divided by how long it takes them to retrieve it (3.5 - 4.5 hours).
If it takes them 4 hours to retrieve your 3TB, then your peak hourly retrieval rate would be 768GB / hour (3072 GB / 4 hours). Your billable hourly retrieval rate would be 768GB - 1.28GB (3072 * .05 / 30 / 4 hours).
Total retrieval fee: 766.72 * 720 * .01 = $5520.38 (~180x your monthly storage fee)
The pricing appears to not be optimized for retrieving all your data in one fell swoop. This particular example appears to be a worst case scenario for restoration because you haven't split up your data into multiple archives (doing so would allow you to reduce your peak hourly retrieval by spacing out your requests for each archive) and you want to restore all your data (the free 5% of your data stored doesn't help as much when you want to restore all your data).
A spokesperson for AWS confirmed this for me for an article [1] I wrote for Wired: "For a single request the billable peak rate is the size of the archive, divided by four hours, minus the pro-rated 5% free tier."
If it takes them 4 hours to retrieve your 3TB, then your peak hourly retrieval rate would be 768GB / hour (3072 GB / 4 hours). Your billable hourly retrieval rate would be 768GB - 1.28GB (3072 * .05 / 30 / 4 hours).
Total retrieval fee: 766.72 * 720 * .01 = $5520.38 (~180x your monthly storage fee)
The pricing appears to not be optimized for retrieving all your data in one fell swoop. This particular example appears to be a worst case scenario for restoration because you haven't split up your data into multiple archives (doing so would allow you to reduce your peak hourly retrieval by spacing out your requests for each archive) and you want to restore all your data (the free 5% of your data stored doesn't help as much when you want to restore all your data).
[1] https://forums.aws.amazon.com/message.jspa?messageID=374065#...