Enthusiast in this contest more or less means you are excited enough about something to get a level above what normal people should get and just below professional pricing. An enthusiast camera body can be 2000 euros.
I would say an enthusiast computer is 2-4k.
It really depends what you meant with minimum salary (yearly?) because paying 3 months of salary for a computer like that isn't far fetched. You're not using this to generate recipes for cookies. An enthusiast level car is expensive as well.
Apart from cities with crazy density, you underestimate how much solar we could put in the city outskirts, and it would be fine. We have already the power lines anyway to bring electricity from power plants that are far from those apartments you mention.
There are quite a few OS projects saying that they will prioritize bugs that affect sponsor. And even here on HN it's not a rare comment 'If a company cares about it, they could pay somebody to fix the bug`.
In the Clojure community we have Clojurists Together [0] which is just a program that allows both companies and individual (at different prices) to contribute funding the development of Open Source projects. I think that model works quite well.