But the thing is you can't find any 500gb 2.5" SSD for less than the M.2 I liked above. And 120 GB is just what I linked, you would obviously need more than that.
Yes maybe, however, I'm not aware of all prices acorss all sale platforms throughout the world and I was rather making a point about no difference in data bandwitdh when we're talking about the same interface.
No matter what you use to connect the drive to SATA, the interface, or port if you like, SATA III bandwidth is the same. When M.2 drive works at SATA III speed it doesn't really matter if you connect it via cables or 'more' directly into PCB tracks via the M.2 port.
Also there's a reason there's nothing cheaper than the M.2 in question, if in fact there isn't any anywhere else. In terms of capacity it's smaller than anything really practically useful unless OP wants a Windows machine with just MS Office for example. As far as quality goes it is not the best choice, at least not for me personally.