I think these forums are good. Use Craigslist and Facebook Marketplace too. I think those three will help out. It comes down to price too. 2018 are coming out so guys are excited about those. 2017 are $6000-$7000 off new. Plus the time of year going into winter for much of US.
Invoice pricing is out there, not hard to get. Dealer has holdback of 3% of MSRP normally that they can work with below invoice. If car was $50,000 then there would be holdback of roughly $1500 so a car $1000 below invoice would still be in the realm of dealer holdback. If Stang was $60,000...