How much should I pay for a good ND filter?
Most good ND filters start at around $100 and go up from there. Resin filters, like Lee’s Grad ND filters are generally cheaper than glass filters, like Singh-Ray, or 10-stop solid ND filters. However, once you cross the $100 barrier, you should be looking for performance (is the ND filter truly color neutral, does it cause serious vignetting, is it accurate to the advertised density?) rather than price as an indicator of quality.