I'm currently in a little bit of a DIY kit frenzy, and while i'd like to have them in nice boxes eventually, it was slightly annoying to have them as bare circuit boards when i was not actually soldering things. On the other hand, i don't really have too many tools (and certainly not enough, you never have enough!) So i went for a minimalist setup - everything here is off the shelf, and precut, but there's nothing stopping someone from doing everything from scratch, or boutiqueing up the parts for a more permanent solution.
Step 1: Tools, Parts and Such
As you can see, the tools needed are fairly simple. I'm using 10MM by 10MM by 6mm, pre-cut MDF as a backboard - its very rigid, can be drilled with hand tools and cost me about 2 singapore dollars for 6. You can probably reuse it for future projects too if you don't permanently fix the standoffs. You will also need a pin vise with a 3mm bit (i'm using a tool i got at a local store that's basically a fixed bit pin vice) to drill the holes in the board
You will also need an appropriate number of M3 brass hexagonal standoffs and screws - the same number as the circuit board you're building. You should also start on this *before* you solder everything on the board, but i've done it after so its possible.
My tools cost about 4 dollars, and i spent around 2 on materials - which isn't bad since these are reusable
Step 2: Drilling Accurately
I'm using a pin vise here since i don't need a lot of speed, or force. Using the circuit board as a template means that i can get all the holes perfect. Place the PCB on the MDF board, and push down the pin vise to mark the location of each hole. Then drill a hole straight down on each location. Naturally you really shouldn't do this with a fully populated PCB, but you COULD if you needed to.
My pin vice punched through the wood a little messily so i cleaned it up with a craft knife. Presumably if you wanted to use bolts to secure the standoffs, you might consider countersinking or otherwise partially widening the holes
As you can see, the standoffs fit pretty neatly into the holes, and won't come off without some gentle persuasion. At this point checking if we got the holes right would be a good idea - place the circuit board over the standoffs, and eyeball to make sure things are aligned. If not, well, starting over might be a good idea, or additional holes.
Step 5: And That's All Folks
Now, pop the m3 screws into the holes, screw the standoffs in, and pop them into the holes that were drilled earlier - and that's all there is to it. In addition, the mounting board could also be used as a template for drilling for mounting the PCB in a proper case, or you could epoxy or otherwise fix the standoffs to the board, and mount the whole board in a case.