You should base the cost off of how Rackspace does it (if you aren't already using them ;).
$10-$15 / 256mb / month
$20-$30 / 512mb / month
Thanks for the feedback Ben. We asked for percentage mark-ups in the poll about Amazon EC2 pricing. The difference in this poll is that we're trying to get a sense for what people feel is reasonable in absolute terms. It's a similar question just from a different angle that might appeal to different crowds.
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