Which NDT method?
I can share with you that over the years we had many requests for NDT estimates. The majority of these came from ASME code shops and usually RT was the method our customers were interested in. They did not use weight, rather footage of welding. There were usually too many variables to make the cost per foot reliable. If you are using MT or PT it might be easier to come up with a cost estimation, but I don't know if weight can be a factor.