Well, as we all know that currency is not stable and will change on a regular basis. So, I suggest, instead of using USD as the only currency standard, can we also have a limit based on euro? This way, even if the currency fluctuates, it shouldn't have any issue.
I.e 7 usd or 5.5 euro?
Take this for example,
http://www.lowendbox.com/blog/rootnerds-e5-50month-256mb-openvz-vps-in-frankfurt-germany/#comments