I'll tell you because I talked to the dealer extensively last weekend about a failed rear turbo (actually the right hand turbo). They said it was a 6 hour job to replace the rear turbo. Here they charge $121/hour labor so that's $726 just for the labor. They also suggested I replace both at the same time and labor if you did both at the same time was 8 hours total or $968. Then the cost of the RH turbo is $573 after the core deposit. So for just the turbo and labor it's right at $1,300 and then you also have the additional cost of new coolant, washers, nuts, and gaskets. Overall it was going to be about $1,500 to replace just the rear turbo.
If you did them both at the same time I would expect a repair cost of ~$2,300.
I currently returned my turbo to Ford and I'm waiting on them to have the new one delivered. Apparently they are currently in the middle of a part number change and it could be up to 5 days before I get my turbo. In order to remove the turbo you have to drop the front subframe, remove the downpipe, I used the flex pipe and zipties to move the midpipe out of the way, drain the coolant, remove strut bar, remove various vacuum lines, remove the charged air line (from turbo to CAC), remove oil supply and return lines, remove coolant supply and return lines, remove lots of bolts that hold in various heat shields (that are going to be a PITA to get back in), and then disconnect the turbo from the exhaust manifold and mounts and take it out the bottom. Hopefully you have small hands like I do or else some of the bolts are going to be hard to remove. There were times where I was literally laying on the engine so I could see down the firewall.
It is definitely not a quick or easy task. I would say the hardest parts are removing any of the nuts/bolts on the exhaust including manifold to turbo, removing the oil supply line from the block, removing the ball joint without damaging it, and re-installing bolts is going to be terrible (since you can either see what you want to do or have your hands where you want them, not both). Overall it's going to cost me about $700 in parts/gaskets/coolant and probably 1 week of my own labor.
If you're going to do it yourself, I also suggest changing he PTU fluid while everything is removed. With the subframe and downpipe removed the fill hole is right there and it's EASY to put in a tube to pump oil out for replacement.
