Here is a Gen2 16s. If he had 3, I’d buy them myself. 
Can’t find a 2015 6s right now to go with it. Should be able to find one for $300.
2012-2013 not the best choice. Hold out for a 15 or 16.
Super easy drop in combo. I have harness and monitor that works.
I may just talk myself into it, but I double the price for my efforts. 