Since an SSD doesn't rotate or move an arm, it's not likely to need much to secure it, no vibrations to try and prevent either nor any requirement on mounting orientation.
Point is, the uber-cheap way if you plan ahead is to just drill some corresponding holes in your case bay with a drill, on the near side of the bay. Far side of drive need not be secured, with a couple of tight screws on one side it's not going anywhere.
Option #2, drill those 2 holes anywhere you want, floor of case, front wall, rear, no need to take up a whole big drive bay just to mount a 2.5" SSD.