If you have to ask.....
Mechanical disks *should* be no more difficult to install than normal V-brakes or even cantilevers for that matter. It's just a matter of cutting some cable and housings, etc.
But for somebody who has probably never installed anything more complicated than a blinkie light or a ding bell and tassles to a bike
, you'd probably be better off paying the LBS to do it for you.
Or not. After all, they're only brakes, and all they do is slow ya down - who cares if they actually work or not?