How Much Should This Cost?

I am installing low voltage lights in a cabinet. The transformer (12v v magnetic) is simply a black unit 3 inches by 6 inches with a set of black and white wires on 1 side (120v), and two white wires on the other end (12v). I would assume that the 120v connections (to romex) must be in a junction box. How would you place them in a box? Normally, romex is clamped by the little clamps in the box, but these wires are unsheathed.

we just had an addition put in our house and as an afterthought want to install a ceiling fan in a room replacing one of four flush-mount ceiling lights with the fan. but three of the lights were wired to the fourth which goes to the wall switch. so if we installed the fan we could never have it on without all the lights on. we thought that instead of having to rewire/fish/break dry wall that it might be possible to install separate on/off switches on these ceiling lights so that they can be controlled independently of the wall switch - is this possible? i have looked around and have not yet found ceiling flush mounts that switch separately any other solutions, or are we stuck with getting an electrician in again? tx for your help