I am sorry if that is confusing - it is not in any way meant to be a dark pattern or misleading.
We can't charge people, for instance, 30 cents per month (as in your example) - the fees or processing your card (or paypal payment) would be larger than that.
The minimum order of 500 GB computes to $10 per month. If you have a very tight budget, please email info@rsync.net and I will personally figure out a way (annual payment, whatever) to make it work for you. It will be larger than 15 GB, however, unless you want to pay 5 years in advance.
I was just about to change the wording on the pricing page to be "500-9999 GB" but that's even more confusing, IMO ... I think most people understand that processing fees dictate a minimum order ...