difficult question to answer because it comes down to personal background, equipment you own, cost & time
Don't know about shopsabre or how easy the job would be but I have an old gerber system 48 so machine isn't manufactured anymore & absolutely no support from Gerber. My PC router was beyond repair & PC are not so easy to purchase or deal with in UK so I purchesed a spindle & mount to fit to my machine.
The z axis set up using the PC router had to be modified a bit to enable me to fit the new spindle mount, this involved making a new Aluminium plate which was drilled for the new mound & then drilling to fit the old mounting point on the z axis. I needed to be able to measure & drill accurately to be able to do that but having an engineering background & access to suitable equipment it wasn't a problem.
So it comes down to the start of my post, do you have the ability to do something like that if required, if you already have a cnc up & running then you already have most of the equipment side covered
If you do & you have the time then you will probably save money
If you don't then I would guess shopsabre can sell you everything you need & it would be more of a nuts & bolts job which would be much quicker but at a higher price but with the added advantage of having a company you can call for help if you have problems.
Do shopsabre have their own forum you could ask this question on ??