I had all the needed items at home, so it was very cheap to build.
It also turned out to be very sturdy and reliable during a few bike rides.
Items you'll need:
* shoe shine sponge box (here are a few models),
* zip ties
* rubber band (or piece of elastic strip with a locker - check first link)
* self adhesive felt pads (like those you put under chair legs and other furniture)
* self adhesive velcro (glue one part on the back of the gps and the other on the sponge box)
* piece of rubber or anti slid material
1 - make 8 small holes on the plastic shoe shine box ( photo #1 )
Four of them will make a small square on the bottom center of the box. Leave 1.5 to 2cm between them. This will allow the box to be centered when attached to the bike (and you can choose to mount it on the stem or on the handlebar).
The other 4 holes (red dots) is where you will pass the rubber band / elastic strip through. Put the GPS in the box and check for the best positioning of the rubber band. Remember its purpose is to keep the GPS secure, so you don't the holes to be too "high" on the box.
2 - ( photo #2 ) Center the GPS inside the box and glue a few self adhesive felt pads to fill the space between the GPS and the box, thus helping to keep the GPS in place. ( My GPS has velcro on the back and it "glues" to the felt pads on the bottom of the box ).
3 - ( photo #3 ) Use the zip ties to secure the box on the handlebar (or stem).
You may consider putting a piece of rubber or anti slid material between the zip ties and the handlebar to increase friction and absorb vibrations . This will help keep the mount in place. Make sure you test the mount orientation by putting the GPS in it and tilting the mount up or down to increase readability. When you find the optimal position, secure the zip ties.
4 - ( photo #3 ) Cut the rubber band or elastic strip and pass it through the holes near the box rim. Tie a knot so it remains in tension. If you're using the elastic strip, you can use a locker instead (see photos on the original mount - 1st link in the text)
5 - ( photo #4 ) Put your GPS in your new homemade mount and go ride around town :)