The new billing system charges per hour used of resource, it's a slightly different approach than packages. If you now are using a 'subsonic' instance (1GB RAM and 1vCPU), with Predictable Bill you'll pay at most $4.50 each month for that instance. Differently from the previous billing, if you need to run another 'subsonic' or larger instance, you can do that and get billed for each hour it runs up to 600hours in a month. Any hour after 600 is on us, we don't count them.
The US-East 1 and US-East 2 clusters have different prices given the different architecture. US-East 1 is cheaper but has spinning disks. On the other hand US-East 2 has all SSDs and Intel Xeon processors, boot times in the 30seconds range.