Ulev means ultra low emissions vehicle and I believe there's not really a horsepower difference. I believe they're the same but the f23a4 might be slightly less
F23A4
This engine was used in the 1998-2002 Honda Accord ULEV models. It is substantially similar to the F23A1, but features ULEV certification with a slight reduction of power: 148 hp (108 kW) with a maximum torque of 150 lb·ft (203 Nm). This engine has a different exhaust manifold, a more restrictive intake manifold and cylinder head, and a 32-bit ECU which uses an AFR (Air Fuel Ratio) oxygen sensor when compared to the F23A1.
I mean, theoretically, even though it had less power, it had beefier exhaust components, more restrictive head, etc, the ULEV should cost more but they were probably about the same price more or less.
Indeed, the ULEV model was designed to comply with strict CA emissions for the US. The engine has a slight power reduction but at the benefit of lower CO2, as far as value goes it seems that the cost was the same as LEV models.