Your problem here appears to be that you are trying to budget third-party services as if they were equipment costs. You'd be better off treating virtualized services as a service or utility, and estimating those costs the same way you would electricity usage or shipping costs.
Cloud Services Aren't Capital Investments
If you buy a server or build a server room, that is a capital cost. You then have some tangible asset subject to first-sale doctrine, depreciation, and all the other ins and outs of owning material equipment.
Cloud services (regardless of type) aren't something you own. They are a service you rent by time (e.g. X dollars per calendar month) or usage (e.g. Y dollars per minute of use). You don't own the equipment, you haven't bought anything tangible that you can sell or depreciate, and most support is outsourced to the cloud services provider.
In other words, cloud services aren't hardware from a customer's point of view, so calculating hardware or hardware-maintenance costs for a cloud service (unless you are running the cloud service) is a no-op.
Projecting Costs for Cloud Services
Calculating costs for cloud services can be difficult, as the market is largely a confusopoly. Nevertheless, you can certainly evaluate the service terms and make projections about your project's intended usage.
For example, if you plan to run 20 minimalist Digital Ocean droplets for your project, you can estimate your server costs at $100/month and your labor costs at whatever you think it will take your team to perform systems administration on the droplets. That's your total cost of ownership (TCO).
If you're using a service where you pay by the megabyte or the minute, then you'll need to estimate your project's intended levels of utilization. That may be a bit less straightforward, but it should still be possible to come up with an expected range for planning purposes. Just don't forget to add in your team's administration and support of the service to calculate TCO.
Estimates Express Expectations
If you want a hard target, just go with your upper bound. For example, if a service costs $0.05/minute, then the service (exclusive of your other administrative and support costs) will come to $504.00/week at full utilization.
Maybe you expect to only use 50% of that capacity. Or maybe your usage will vary between 30-60% from week to week. You can express those sorts of figures as a range, a statistical average over time, or whatever else makes sense to report or budget for in your organization.
You can always refine your estimates as you gain knowledge of the project and its resources. Continuous refinement is essential for effective project management.