One of the challenges is that, with rare exceptions, cities don't build out in advance of demand and, once the demand is there, rebuilding housing, transportation, and other systems is often expensive and disruptive--and can really be hard without a strong central authority.
Singapore is probably about as good an example as any (at least outside of China) of centralized urban planning (and they even have an interesting gallery on it https://www.ura.gov.sg/corporate). But, while getting around Singapore works pretty well, it's certainly not a city you would call especially affordable in general.