That is incredibly cheap. It's the sort of cheap that's so cheap you wonder what the catch is.
Assuming a perfectly spherical developer, you're at $100,000/year. You're using Xamarin because it makes that developer more efficient because (1) you've determined C# is an easier language to maintain and/or (2) cross compatibility is worth something. If this developer is just 1% more efficient, you've paid for your Xamarin license. If he's not 1% more efficient, why are you even using Xamarin in the first place?
Er, that's on top of your Windows license, your Visual Studio license, your Apple Developer License, your Apple Macbook because you can only compile and deploy to the app store with a Macbook... oh and Xamarin university if you want to become certified... and if I understand the terms correctly, it's not $1000 per developer, it's $1000 per developer per platform, so if you want iOS and Android, it's $2000 per developer on top of all that previous licensing. So to say it's incredibly cheap at $1000 isn't the whole story.
You don't need a MacBook. You can develop on Windows (which means you don't have to pay for that Windows license) and use a Mac Mini on the network for the OS X build requirements.
That is incredibly cheap. It's the sort of cheap that's so cheap you wonder what the catch is.
Assuming a perfectly spherical developer, you're at $100,000/year. You're using Xamarin because it makes that developer more efficient because (1) you've determined C# is an easier language to maintain and/or (2) cross compatibility is worth something. If this developer is just 1% more efficient, you've paid for your Xamarin license. If he's not 1% more efficient, why are you even using Xamarin in the first place?