I would as a guesstimate say your in the $30k area, depending on variables. Here is a website you may want to check out. http://www.shot-stop.com/Pricing.aspx
I would imagine mining the lead at the base of the shot curtains over a period of time would make it well worth the investment ... It would also give you a consistent back ground and probably eliminate some of the wind effects, though not completely ... I see a need for a few charts and graphs to show the increased percentage in mining and the effect of wind ... WPT ... (YAC) ...
I think the shot recovery would make a great cost savings, as the Shot would fall into the CUFF of the fabric at the bottom, and an Industrial Vacuum would make reclamation easy, you would need several 55 gal drums to pour shot into from the vacuum, and then containers that would hold 25lbs of shot for re-sale. GB......................DLS