All accounts get 7 days (as the parent shows) and all 1TB+ accounts get 7 days + 4 weeks.
However, if you want a custom schedule (say, 30 days, 8 weeks, and 6 months) it only costs more if the space they use exceeds your existing account.
So, if you have a 100 GB account and you use 60 GB and your fancy snapshot schedule (of which the first 7 days is always free) only uses 35 GB ... then there is no additional cost at all.
Also, note that 1TB accounts are 15c per GB, per month, and 10TB accounts are 7c per GB, per month - all with no traffic or usage costs.
This compares very favorably with S3 and blows the mozy pro pricing out of the water[1].
https://news.ycombinator.com/item?id=6554313
(I happen to get a discount for being a prgmr.com user, but IIRC the terms are similar.)