On a dedicated server $12.50/mo barely covers the space and power to say nothing of bandwidth, hardware, support, etc.
I would recommend either looking for storage only options, or upping your budget a bit.
Blatant self promotion here, but we have an CloudStack platform running in Phoenix if you ever want another stateside option.
Also thanks for once again pointing out how DO and Vultr are trying to gain some sort of marketing edge calling themselves cloud instead of vps. True there are no set...
They have an open source edition: http://www.mailcleaner.org/
Though it appears it hasn't been updated for 2 years, which is almost exactly as long as its been since i've looked into it. (Did a fabulous job at the time though as a total drop in replacement for the barracuda that dropped dead)