Is infill more costly?

Recently I saw an argument on X that went something like this:

Person A- infill is cheaper than sprawl because no one has to build new sewer lines!

Person B- Sprawl is cheaper because its more expensive to build in the city!

Person B’s post made me wonder: is suburbia always cheaper?

I decided to do a rough comparison: the cheapest new city houses vs. the cheapest new suburban houses of the same size. I went on Zillow and searched for houses that were a) built after 2020 and b) 2000-2500 square feet.

In some metros (even fairly inexpensive ones), suburbia clearly did seem to be cheaper. For example, the cheapest new house in Chicago started at around $600k, while similar options in Lake and McHenry Counties started at around $360-370k. In St. Louis, the cheapest new home cost around $450k, about a third more than the cheapest new houses in St. Louis and St. Charles Counties.

On the other hand, I found counterexamples. The cheapest new house in Atlanta cost $290k, about 15 percent below its counterparts in Cobb and Gwinnett Counties. The cheapest new house in Houston cost $225k, about the same as its counterpart in suburban Fort Bend County. The cheapest in Cleveland cost $288k, about the same as its counterpart in the suburban part of Cuyahoga County, slightly less than its counterpart in outer-suburban Lake County, and about 25 percent less than its counterpart in outer-suburban Geauga County. In Philadelphia, the cheapest new house is about $350k, about 10 percent lower than its counterpart in outer-suburban Chester County.

All of this is subject to two qualifications. First, this is not an academic “everything being equal” comparison: all I am trying to show is that it seems possible to build urban and suburban houses for similar prices. Second, it may be that at the true outer edges of suburbia, houses are cheaper than in the suburbs I have mentioned.