[JackG]

His math doesn't add up.

$400 for two new axles, installed.
$170 each for the axles x 2 = $340
That leaves $60 for labor. ???

$525 for four new boots on your axles.
Let's say $100 for boots
That leaves $425 for labor.

Pulling and re-installing the axles is 90% of the job, and you have to do that for both options.
Disassembling the axles, cleaning the CV joints, and re-assembling with new boots may take an additional 1 - 1.5 hours. (I've done it, I did the DIY writeup)
This guy must really hate cleaning CV joints, or is getting the new axles for free.

Having said all that, $525 for the boot job isn't really that bad. If you won't, or can't, do it yourself, that's what I'd do.