You're wrong, on both accounts. It has smeg all to do with billionaire owners, Utd aren't sustained by billionaire owners even if they are that rich. Utd bring in that much money every year, as do Barca/Real(to a degree, their tv deals in La Liga are patently unfair in every single way you can think of).
30mil transfers started happening in 97-98, how much did Ba or Cisse cost? How much was Kompany, how much was De Jong, 18mil when he only had I forget if its 6 months or year left on his contract, but it was get him for 18mil then and there or wait, get someone else they didn't want and have a lot more competition for De Jong on a free transfer.
Transfers fee's still range from tiny to huge, and it is sustainable because the vast majority of the money comes from advertising, though directly through tv deals the money those broadcasting companies pay is from advertising. Football is one of if not the most watched sport in the world, billions of people pay to watch it, advertisers worldwide pay billions to advertise on peak tv. TV money in the early 90's was next to nothing, tv money today, well, okay in 1-2 years a new 3billion deal is already done.
You can get some crappy car for £6k, or buy a Ferrari for 500k, you can buy a tiny flat/house somewhere crappy for 50k, or buy a multi million pound mansion where you actually want to live. You can buy a footballer for free, or you can pay whatever you want for one. Ronaldo has directly led to titles being won, millions upon millions in sponsorship deals that are vastly increased in value because Ronaldo is part of the Real Madrid brand at the moment. It's an investment, not just peeing money down the drain.
As with EVERY OTHER INDUSTRY WORLDWIDE, some investments prove to be fantastic, some prove to be horrific.... can you explain why football should be lots of business's running completely risk free, while the rest of the business in the world isn't?