Sure, and most of those imports would come from the surrounding farmland. It would likely be somewhat more expensive than the current system, but primarily because urban taxes would not be providing agricultural subsidies.
Tokyo already does this and food there is not substantially expensive than it is in other alpha cities.
Also there are plenty of big cities not surrounded by farmland. Hong Kong and Singapore, for example.
Locally-grown food is generally more expensive in these areas because smaller local farms do not enjoy the same advantage of economy of scale that global distributors do.
interesting you missed Tokyo there. Japan imports 100% of food consumed regularly except for rice, which is expensive compared to overseas (about $5/kg). Other locally grown meats fruits etc are generally premium items.
