Well, that heavily depends upon factors like what kind of lifestyle you're living. For example, I save a shitload of money by not needing a car.
In general I'd say that someone who lives in my town and makes roughly what I do could save 1k to 2k per month depending on how much discretionary spending they want to be able to do. Possibly more if they're very frugal.
In case we're comparing to the USA here, Germany has lower wages and higher taxes but a lot of stuff is way cheaper, especially education and healthcare. My health insurance premium can't exceed 14.6% of my income, deductibles don't exist, and most procedures are fully covered – for instance, when I went to a hospital for surgery and stayed for four days, my total bill was 40 €.
If Microsoft had added an Android app runtime (even if it were slow), they would've had a much better argument for buying Windows phones. As it was, their sales pitch was "buy a phone with this new OS that doesn't run any of your apps, from the guys who made WinCE" (Windows Phone) and "buy a phone with this new OS that looks exactly like the last OS but won't run apps from that one or Android" (Windows 10 Phone).
By the time Win10P dropped, nobody expected Microsoft to actually commit to it (so the enthusiast crowd stayed away) and its app ecosystem was literally a decade behind the competition (so casual users wouldn't touch it). And then Microsoft didn't see sales and promptly canceled the whole thing.