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Summary: Although you can probably use (a combination of) photographic neutral density (ND) filters to reduce the same amount of light as a typical solar filter (e.g. Baader solar filter), it is not SAFE for your eyes as it will not filter out the harmful Ultraviolet (UV) and infra-red (IR) light.

The table below shows the reduction in light intensity obtained by using different filters — both photographic ND filters of various Optical Density (OD) and the Baader solar filter. Just from the standpoint of intensity reduction, it is evident that one would require a 12-stop ND filter (OD 3.8) to match the Baader Photographic AstroSolar film. However, the following reasons undoubtedly makes the photographic Neutral Density filters unsuitable for solar photography: 

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