VPS Pricing - How is Charged?

Okay so I’m currently on the free trial, but I’m wondering how exactly the VPS pricing is calculated; I notice that at the bottom of the resources page it lists what memory limit has been set and when/how long, are the charges based on this time or is it simply the highest setting for the month? i.e - if I increased my limit from 600mb to 900mb for a week to test something, would I pay the 900mb price for the entire month, or just for that week with the 600mb price for the rest?

Also, I have listed on the total price a $10 subsidy per month; is this permanent or is it part of a limited offer?

I’ve had a VPS for several years now, the charges are only for the time used. Thus if you have 600 MB for most of the month and 900 MB for one week in that month, you’d just pay the 900 MB rate for 1 week and the 600 MB rate for the rest of the month.

In your VPS cost overview it would show how much you paid exactly for each period that you had a certain MB limit.