Create a Rectangle around a point in PostGIS

The ST_Buffer function will buffer the specified distance in the units of the geometry's spatial reference system. In your case, you are effectively asking to buffer a distance of 152.40 degrees, which is not really what you want to do.

Also, buffering around a point will create a circle and not a rectangle. To get your rectangle you can instead use the ST_MakeEnvelope function which requires you to specify your minimum and maximum x and y extents which you can determine from your point coordinates.

If you want to work in units of feet or meters you will need to project your points to a projected coordinate system that uses feet or meters. This coordinate system will depend on the extent of your data; if it covers the contiguous USA you could use the US National Atlas EPSG:2163, or if it is more regional you should look into the US State Plane projections and UTM Zones. Of course you also have to consider the accuracy you are hoping to achieve.

The following SQL example constructs a point geometry in WGS84 before transforming to the US National Atlas projection and determining the minimum and maximum x and y extents. Since the point is going to be the centre of the rectangle these extents are calculated using half of the intended length/width. Additionally, since the US National Atlas projection uses meters I've converted the 250 feet to the corresponding distance in meters.

SELECT 
ST_MakeEnvelope(
    (ST_X(ST_Transform(ST_SetSRID(ST_MakePoint(longitude,latitude),4326),2163))-(250/3.28)), --Min X
    (ST_Y(ST_Transform(ST_SetSRID(ST_MakePoint(longitude,latitude),4326),2163))-(250/3.28)), -- Min Y
    (ST_X(ST_Transform(ST_SetSRID(ST_MakePoint(longitude,latitude),4326),2163))+(250/3.28)), -- Max X
    (ST_Y(ST_Transform(ST_SetSRID(ST_MakePoint(longitude,latitude),4326),2163))+(250/3.28)),  --Max Y
    2163
    )

There is certainly a much more efficient way of constructing the SQL but hopefully this illustrates the points above.