Read what they're offering - You're saying 10GB of network transfer, but you're saying actual is 300M. That's actually 0.03 * 0.75 = $0.0225
Read the example above the ratecalc if you don't believe me - They actually charge you per token (KB-minute) for disk and RAM.
Unless you're using the KVM option, you're usually doing OK. For example:
You say 1GB of RAM, but you're very unlikely to have that sort of commit set; they're not charging you for I/O cache, unless you're using the KVM virtualised stuff instead of the vserver based infrastructure. So on a typical Apache2 + PHP + PostgreSQL load, you're probably only up to about 200M - So that's actually more like $5/month.
And what are you saying about 15G of storage at the top - that's loads! But they offer you a bunch of preinstalled software that isn't counted in your disk usage, and above that you are only charged as allocated. You don't have to say in advance "I want 15 GB". If you're just using, say 2GB, then it's actually only $2.62.
Now, here's the bad news: the minimum you're up for is $20/month, so that's how they hit you.
Cheers,
Michael