I had the same experience -- that is, they offered to do both tone rings for an extra $100 and tried to sell it as the smart thing to do and a great buy. I declined (nervously) and just had them do the broken one. That was years ago on my 06FEH and the other tone ring hasn't failed yet.
The trouble is, if we go ahead and do both, we never know what might have happened. I'd be willing to pay the extra $30 (and a second trip to the dealer) to find out. And I did (find out, that is). I saved $100.

 

I'm being quoted 718$ at a ford dealership to replace a rear cracked tone ring because they are sold "as a unit". When I countered that, I was told it was because the rear axle is rusted and they would have difficulty putting a new tone ring on it. Car is 2006 but only 32K miles on it. Am I being taken for a ride by my Ford dealership? I spoke to the manager who just turned me over to the service manager, who hasn't gotten back to me.

 

It stands out that you have a 10 year old car and only 32K miles. It's a know fact that cars don't like to just "hang out" doing nothing. One of the reasons that Taxi Cabs last so long (mileage) is that they are constantly in use. Cars little used can easily build up rust that a heavily used one would not.
The tone rings were a poor idea and made Ford Service a lot of income. They got some of mine on a front end tone ring on my 2006 FEH. But now I have a 2010 FEH and it's not an issue. (And they tried to get me to do both with the same scam -- I refused and didn't have trouble with the other one.)
Keep after the dealer ... I find it pays benefits.

 

I think that $718 is a huge rip off. Take it to an independent shop and get an estimate for replacing just the tone ring. There is a reason that they call them "Stealerships".

 

Given this is a hybrid, is there anything on replacing the rear tone ring with the rear half axle that would be difficult for a non dealer to do? I understand the half axle part is specific to the make/model of the car, because my dealer didn't have it in stock, and couldn't order it or even an aftermarket part, for 3-4 days.

At another dealer, I was quoted 360 for the tone ring if they don't have to replace the axle, another almost $400 for the half axle if it "falls apart due to rust" and maybe $250 if they had to "burn some bolts off" also due to rust. I told them I would think about it.

So assuming the half axle does need to be replaced (now I read that hundreds of thousands of Escapes up to 2004 were recalled for chassis corrosion problems - so I would not be surprised if the 2006 are as bad which may account for the rust is there anything complicated about the Escape hybrid that would give an independent mechanic pause, or if they do something wrong would cause a major problem a dealer would have to fix?