also phonegap is free, while xamarin.android and xamarin.ios have high license costs for developer and platform

https://store.xamarin.com/

Not the whole story... Xamarin have a Starter Edition that is free for both platforms; admittedly with limitations (maximum app size, no linking with 3rd party code other than Xamarin provided assemblies and the iOS SDK). Within those limitation, you can publish to the App Store with the Starter Edition (obviously you need a Mac as well for iOS). The Indie Edition drops both of those limitations for USD299 per annum, which is reasonably affordable from my perspective. (Disclaimer: I have paid for the Business Edition; USD999 per annum, which adds the ability to use Visual Studio and a few other things).

The app size limit is so restrictive their own demos won't even compile. It's a tremendous shame because they automatically exclude so many people.

That's 300 dollars per platform right? So 600 dollars if I wanted to create an android / ios app?

More or less

you get a 10% discount on the total price if you buy multiple licences at the same time

You can see all here: https://store.xamarin.com/#purchase

The cheapest PhoneGap offering with support will cost you at least $249/year. And for that much you get No Guarantee support, which sounds quite odd.

As i see in the link above the support for xamarin is only in the business package so it starts at $999/year (please correct me if i am wrong).

Anyway i was not talking about the support option, but about the chance of deploy a full serious multios app. With phonegap you have that for free, with xamarin you have to pay (299*2) minus discount of 10%. Just this.

wrong appcelerator doesnt use CSS/HTML , just javascript. The UI is native with appcelerator.