Near is one of the geoprocessing tools and you have options for its usage:
Using geoprocessing
Geoprocessor managed assembly
It sounds like you will be working with a couple of specific geometries. The geoprocessing tools in .NET do not support the input of a geometry directly. It must be contained in a feature class or feature set for example. However, most of the geoprocessing tools will honor selection sets on input layers and this is typically how you would work with a single, or reduced set, of features from a given feature class when using the geoprocsssing tools in .NET. In Python serveral convience methods are provided to assit you with direct input of geometires.
Another option would be to use IProximityOperator. This will allow you to work with geometry objects directly.