My default position for most business tasks would be to do this with Haskell. You asked for the three criteria:
1. Haskell as around for longer time than the other two options. It will enable new people to quickly grasp your code base, so even if some core members leave the team the system will support them actively.
2. A true winner. Haskell allows for using very abstract and generic code. If this works then it can be used in many contexts. In Go and Python your devs will write more low-level code that is less reusable. Just think about writing a function that adds 10 to its argument. In Haskell:
add10 = (+10)
You can easily call this to add 10 to a number. You can never make a type error with this. But now: what happens if you are reading numbers from some incoming bad data? You may have been able to read a number or not. In Python you may have a value `x = None` and in Haskell x would be `Nothing`.
In Haskell you can make your `add10` into a very reusable component which we call f: `f = pure . add10` and you can use it like this:
x >>= f
And it will work fine.
In Python you need to write a new function which first checks if its argument is None and if yes it will return None, otherwise it calls add10() on it.
Or you have a list of numbers and we call it again `x`.
To add 10 to each element in Haskell you do:
x >>= f
In Python (and Go) you would have to write a function which will map over x and apply add10 to each element.
What if you now have a function which may either return a number or an error message? In Haskell such a value can be used like this:
x >>= f
In Go or Python you would have to write a function which first checks if x is an error message and if yes returns it or otherwise calls add10() on its argument.
What if you wrote a function `x` which reads a number from the keyboard and returns it? In Haskell you would use it like this:
x >>= f
In Python you will first have write a function which calls x and then makes use of the return value.
In Go and Python you would have to write several different implementations to handle different contexts (absense of values, error handling, IO, DB requests, non-deterministic values, etc) and every single time they would look different. In Haskell this function will always have this body:
x >>= f
And this is only the beginning. Haskell allows you to write less code than dynamically typed languages. But your code will run very fast and have way less errors. In Python every function call needs to be looked up at runtime first. In Haskell you go to the function definition and save much overhead.
From my experience in 2017 with our production system was that nearly every bigger problem was due to some type error. Nearly always! This is what we get from a dyanmically typed language. The initial development time may be a tiny bit shorter, but then you will pay this many times with more debugging time and with time to write more tests.
Only tonight one colleague had to stay some extra hours in the office because there was some strange bug in the Python code.
To outperform the competition you need to write ultra stable code that runs fast. Neither Go and certainly not Python can give you this. For scripting this is of course different. Our data scientists use R and this works fine for them.
But with Haskell you can write very generic code, but without magic involved. In every single case you will know _perfectly_ what situation you are in thanks to the type system.
Your point 3:
If you’ve got such a nice budget go visit some headhunter and try to find out what they have to offer.
I can only say that I know people who are willing to move to get a Haskell job. You may want to consider to have some remote positions. But you may also need fewer Haskell devs because they will be more productive.
One other thing: nowadays Python and Go are pretty common. People learn it because those are popular languages and because the market has a demand. The days when Python was considered an esoteric language are long over. Haskell is learned because people are deeply interested in programming and not out of some necessity to earn money. Those might be the guys you are after.