Well, the Mall of America cost 650 Million. Contains a number of restaurants, fast food joints, and other entertainment.
Now, for a self sufficient city, not all those stores are needed. But what type of population are you looking for?
The mall is 4 levels, if you converted 1 level to housing, added 3 levels of housing, I would guess that would give you about 1000-1500 families housing units. Perhaps more than you need, so maybe only 2 added levels are needed. Which, as a very rough guess, would be about 1.5 Billion.
Fun thought exercise, my guesses really are rough ballpark. So if anyone has any better cost estimates, please speak up
