If I could have bought my 4 bed house with average garden on the outskirts of London for £50k, I wouldn't have bought it. I'd have bought an 6 bed house with a swimming pool, huge garden, double garage and driveway in central London instead, for the price I paid for my house. Not to get rich, just because I'd like more space, a pool, a big garden and a short walk to one of the world's best city's centre.
It's a physical impossibility to build everyone a large detached family home in the city centre, and most people don't want to live in apartments forever.
I believe the real solution is allowing small towns to grow into cities, and building a ton of very fast and effective rapid 24/7 transport so you can ferry people into the urban core of large cities from those cheaper smaller cities. We can scale out fast trains in a way that we can't scale out cycling, walking and cars.
In my mind, the ideal model for a livable megacity is an extremely large conurbation of individually small, walk/cyclable cities with low to mid-density housing, with the cities separated from each other by large public green spaces and all linked together with rapid public transport, and huge disincentives for cars.