You are right, there is a factor of learning that needs to be baked into your consideration but there comes a point where you put a little trust in people who came before you and tell you 'I have done this, I have been where you are - follow me and you will be fine'.
On the flip side, Nat Friedman is incredibly approachable. I am sure if you simply email him and tell him your concerns he will accommodate you with a longer trial period or some kind of money back guarantee, that just how he is.
Think of it another way: how do you plan to grow the next generation of engineers if they can't afford your technology to learn on, but they can download a JDK and a good Scala IDE for free?
Moreover, I'm not sure how you're arriving at a 10% productivity gain without knowing what I'm already working on. It may be 10% compared to Objective C for iOS, but is it 10% for my server-side Scala project?
Lets just get expense out of the way because that argument is actually invalid. For professional devs like us, if you cannot learn something new enough to make a decision on it - in 30 days, then we have bigger problems than license fees.
If that is the case for you then money is not the issue, it is time. Having 30 free days for me to spend learning a tech is a unicorn, it does not exist.
I understand your frustration because there are so many amazing techs out there I wish I had the time to learn but just don't. I made the decision to invest my time in Xamarin when I realized that the custom mobile dev market is slowly eating the custom web appdev market I was doing so well in. I made a conscious decision to make a bet on Xamarin (mainly because I knew C# very well) because I saw value in their approach vs others.
I have been very successful financially in my career so it could be that I look at time and money different than others, especially college students learning CS, but my statements were aimed at pro devs.
(an aside, I think Xamarin offers very steep discounts to students)
You can do the same thing with a trial of Windows which actually lasts anywhere from 90 to 180 days or something.
1. If I'm bootstrapping a startup, That $2000 is easily at least 1 entire year of web hosting, or a new MacBook, or a couple of new servers. Bootstrapping has thin enough margains that $2000 is a large amount of money and runway for a young company and that's only for one dev. Have two dev's? that's even more of your runway gone. $4000 could sustain two devs for two months if they are really cheap and try hard. Xamarin is unlikely to save you that two months.
2. If I'm developing an indie game there are A HUGE amount of cheaper better options available. Unity, Unreal, Cry Tech, cocos2D/3D, or Apportable. All cheaper and better for game dev.
3. If I'm learning how to develop mobile apps with the hope of obtaining a full time job. Then Xamarin job posts are fairly rare, so spending even $600 to learn the dev process and then still not have the skills to get a full time position is a losing value equation.
4. There are cheaper tools out there, like Ruby Motion or Apportable.
I think the Xamarin guys are brilliant and made a great product but I think the value is very limited to existing Dot Net or independent app developers. Yes it makes a lot of sense for those groups but there are a ton of others that the price is a real barrier to entry.
The only way your math makes sense to me is if a start-up only plans on releasing for one platform at first. If you're going to build an iOS app first and only move on to Android if that iOS app is successful than it probably doesn't make sense to use Xamarin.
If you're planning on doing both iOS and Android at the same time (and maybe Windows Phone as well), the added developer hours (same dev or an additional dev) to build the same project in another language instead of sharing 50% of the code and just building another UI would probably cost you more.
I never heard anyone for Xamarin selling it as a game dev solution. IIRC Unity is actually running on the same Mono engine from Xamarin (it's an open source project, but I think they're running it). Last time I checked some of those other solutions had expensive licenses too.
Xamarin is still too new to see lots of job postings looking for that skill. I also think that in the near future companies using Xamarin will use it for LOB apps. That's a big market for .Net developers building desktop software or internal web sites. A transition to Xamarin might makes sense for both these companies and these developers.
The bottom line, products are targeted at specific customers. Xamarin could have decided to go after the start-ups, but since most start-ups are content with releasing an app on a single platform first, the proposition of getting additional platforms with less work isn't that enticing. It's much easier to sell the product to an enterprise as their cost for multiple teams with different skills would be a lot higher than the Xamarin license.
I guess I also made a fundamental mistake in the above sentences. It's not a person, but rather a business that is looking at it. In the .NET world, it's common to have an MSDN license for each developer. Looking at the costs from that perspective and the licensing costs for Xamarin make a lot more sense.
How much time will it save you? Lets imagine your current project to build an iOS and Android app of identical functionality you are estimating at 6 weeks for each platform. 12 total weeks. Lets say that Xamarin tech gives you a 10% boost (it will be much higher but lets be conservative), that means over the 60 business days, you get back 6. Assume you have 8 hours of work per day and you just bought 48 hours of your time. The basic license which does nearly everything most people need is the Indie license and $300 per platform. Six hundred dollars to buy 48 hours of your time back means the purchase is viable if you value your time at more than 12.50 per hour.
If you value your time less than that, you have bigger problems than which mobile tooling to use.
The truth is the productivity factor is much higher than 10% and the license is good for a year, pick up a couple other projects like this through the year and that number collapses. For me this year I will probably do 4 cross plat projects with Xamarin and my productivity diff is north of 50%. The purchase is a no brainer.