I came at this solution after taking care at cost (if your DIY is very expensive it's better you buy it!), efforts (all my hardest project are still waiting to be completed), parts availability (if you have to wait shipment for each part of the design you'll forget for how you needed them, especially with Italian post service) and functionality.
The slide is a "macro rail" for photography which you can find on eBay at about 10$, but I already had a couple of them. The other parts you need, other than the drill, are only:
- a strong spring (but also a big elastic is good)
- some wood boards
- some screws
- a nail
- 5 inch of a little aluminium cilindrical bar (as the ones of the TV antennas)
- a wood base
- and two inches of aluminium pipe (this also isn't so essential)
Oh yes, and also a nice gum-covered toothbrush! You need only the handle so you can use your own toothbrush - yes, it's time to change it! And yes! THIS is essential!