You can get dedicated tenancy instances in AWS, for an upfront monthly cost of ~$1.2k (per account) and about +10% on top of your normal EC2 instance costs.
I ran the numbers back in 2015 and persuaded the previous employer to go for dedicated tenancy with all performance-critical and privacy-sensitive workloads. I was effectively hedging against unknown but practically guaranteed cross-VM attacks to pacify a paranoid regulator.
Then Rowhammer happened. Less than a day later, our contact with the regulator comes to me asking how it affects us. Being able to answer - with absolute confidence - that it did not, was one of the proudest moments of my career. And the turnaround from "regulator comes asking awkward questions" to "regulator is happy and sees no reason to ask again" of less than 48 hours must be some kind of record too.
You get dedicated time on a core while your task is running. For instance t3.medium is 2 vCPUs (because hyperthreading) but as you can see in [0] it's only one physical core.
