What to price a 1970 Super Bird at my friend is getting in a multi car trade

Boy this is tough one! Even ignoring the typical condititon and pption variables Superbird prices have been really up then down the last two years, maybe a little up last six months. I think at any time in the last year a price for a really good car might vary by 30% - can you say risky!

Not sure I would want to trade. Why not just sell all the cars instead of some wacky trade and flip that could go bad?