Eurovision is very expensive, although I'm never entirely sure why. Costs vary, but somewhere around $20m+ is probably fairly close. And from what I can tell, that cost is essentially borne by the host country - the host being the winner of the previous year's competition (the UK stepped in to host for Ukraine last year having finished 2nd in 2022).
But I'm not sure that it's true to say that it would never happen if proposed today. The ratings are insanely good in most countries across Europe. In the UK it's about 10m, which placed it third in 2023 behind only the coronation (which isn't something that comes around that much) and the finale of Happy Valley. And in some European countries it is taken *much* more seriously than it is in the UK.
And it has a bunch of things that continue to work in 2024. Years ago, they transitioned from juries being the sole arbiters in each country to phone lines and now online voting. That means audience participation. And there's the reality-show style lead-ups in many countries that go about choosing that country's entry (Not everyone does this. Someone in the UK just *picks* our entrant these days.)
Eurovision itself is much bigger than just the Song Competition. There are other shared rights that member countries get access to. And these days, a lot of classical music created by various state broadcasters around Europe is shared this way. For example, many across Europe will watch the New Year's Day Concert from Vienna which plays a lot of Strauss waltzes (e.g. The Blue Danube) every year. The BBC Proms are shared across Europe too.
As for the booing - I'm sure that they have really good sound mixers on the programme that means that they can easily turn up or down sections of the audience that are doing anything that they don't like. For a show like Eurovision, you would probably have lots of microphones scattered across the audience that you can mix between. In Premier League football fixtures, sections of the crowd will sometimes sing songs with words that can't be broadcast, and the sound mixer will dip the relevant mics and bring up others. And I'm sure they can "augment" the crowd mix if needed.
Adam