This would be virtually impossible to identify with a high-level of precision. So many variables in play here and obtaining a CPA benchmark with this level of specificity is no feasible.

The best reco I can give is to simply evaluate what the traffic cost would look like to acquire relevant traffic to your domain and then apply assumptions around contact submissions and the conversions. I’d suggest these would be extremely low based on the high-level of qualification, possibly in the 0.05% range as a percentage of the traffic generated.