[DenisM]

The "added expense of MS software" is largely a myth. Windows is about 30% more expensive on AWS than Linux, and most startup expenses are dominated by payroll, not hosting. Choosing a platform on price in this situation is counterproductive - you should chose whatever allows you to iterate faster until your product idea sticks with your customers. As a rule that's a platform you know the best, can find help for most readily, and can hire new team members the fastest. Hiring for Microsoft stack in Seattle is easier than in most other places.

I say "largely" because occasional startup will be maxing out their hardware trying to build next Google or next Netflix. If hosting can become comparable to payroll in your startup, then it becomes a factor in the platform choice.

If that wasn't enough, Microsoft has Bizspark program where the give you a ton of stuff for free for startups.