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Provide RPs with a UI that shows the regular exchange rate, and lets them enter a different exchange rate and start/end dates. During that time, the sale exchange rate takes precedence.
This must also include some way to communicate to users that there IS a sale price, to attract people to the sale. (maybe this? How to Share News, Events & Trainings, and Outages )
Tagged allocations with special rates (for preemptible instances)
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