That's a big giant "it depends." It depends on what your service looks like: CPU intensive, Memory Intensive, Storage intensive? (In reality some unique mix).

That's a big giant "it depends." It depends on what your service looks like: CPU intensive, Memory Intensive, Storage intensive? (In reality some unique mix). You probably won't see a huge savings year one, as you'll be spinning up a lot of new things and have a fairly large CapEx expenditure. Now if your growth pattern is steady/predictable then you should be able to plan out your hardware buys or do a hybrid solution to handle traffic bursts. One of the nice things about running your own hardware is that there are some costs that are easier to control. Don't need new hardware? Don't need to spend on new hardware for example. You also have much more control over your environment so you are able to really optimize your code, and infrastructure so that you don't need to scale as large system wise. But, back to the question on how to model it? You just gotta dig in, and make some educated guesses about performance,test and repeat.