I am trying to find a plan or schematic to build a 120 volt 30 amp voltage regulator/ line conditioner. can anyone help? the items a found on line sell for 300 to 400.

 

I am trying to find a plan or schematic to build a 120 volt 30 amp voltage regulator/ line conditioner. can anyone help? the items a found on line sell for 300 to 400.

There's a good reason for that. It requires expensive parts to perform that function.
It's unlikely you could do in more cheaply yourself.