From a functional perspective Feature and Capabilities and Commercial Support perspective that is provided directly by Elastic there is no Difference between Elastic Cloud direct through Elastic and Elastic Cloud through the AWS Marketplace ... they are the exact same offering, the only differences is in the Commercial / Billing perspective i.e. you either pay Elastic Directly or through the normal AWS Market Place agreements.
The Hourly / Monthly pricing is the same Direct or through AWS Marketplace.
There are annual and multi-year options but you would need to engage with an Elastic Sales Team to discuss.