We offer Managed and hosted EV SaaS solutions as well and use both. They will be fairly similar as far a guarantees and cost. But it depends on what you need to do.
For example say you had a smaller org with a couple of servers for SMTP Archiving, you might be looking ~$450 as month but larger enviroments could be ~$1000 a month. It just depends on the amount of data, what you're looking to do with EV etc. You can use the calculators to esitmate cost:
https://azure.microsoft.com/en-us/pricing/calculator/
https://calculator.s3.amazonaws.com/index.html
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