replacing the axle will cost a lot more money than just replacing the boot.
I agree with X5 Flyboy
CV joints are fairly tough but if there is grit in there it will cause damage .
you do not require a complete axle if you want to replace the CV joint . edit - I just looked up real oem and discovered they sell the complete axle or individual boots only - .
if you read my diy you will see the parts that are attached to each end of the shaft , the outer end has the actual CV joint , as shown held in hand after removal from the shaft .
the inner end has a triple roller bearing which fits into a cup as shown in the last 2 pics borrowed from generx . the cup connects to the diff .
it should be possible to look into the tear on your boot , wipe some grease from one or more of the ball bearings to see if there is any scoring or gouges . if the bearings are smooth you should be good to retain the CV joint .

you really need to read the link to the diy by hayaku to fully understand how it all works because hayaku dismantles and cleans up everything so you can get a good idea of what is in there .
my diy is really just a quick guide to replacing the boot provided you know all the tools to use and torque settings , if not then that is why I recommended reading the link .