Just an example of scaling your speed (this would suit my personal family's usage, we average around 30 and have gone as high as 70 when I was in the last month of my Technet subscription :P).
FS/FS to 30GB
2mb/512 to 60GB
1mb/256kb to 80GB
512kb/128kb to 120GB
It would stop connection abusers while allowing users that want a fixed price and all that.