Hi David,
I personally do not like the domain names, but they may hold some value. I think JFKTaxi or JFKCab would have been better.
I saw a name a few months ago auctioned at Flippa that may give you some rough numbers. The domain was JFKLimo/com and was sold for $2000. The owner advertised it as a limo service for JFK airport. I personally think that your names hold less value that the above mentioned.
My opinion is that JFKTaxis can go for low $$$ to $4$$ if marketed properly (end user prices). Even though JFKCabs is essentially the same thing as JFKTaxis, I do not see any real value in it. (Try to sell them as a package)
As I told you in the beginning, the singulars would have been a lot better as far as I'm concerned. Try to market the names to any taxi service at JFK airport and see how it goes. Here's a potential end user: jfktaxiservice.com
I am sure you can find more.
Good luck!
Radu