What can you use instead of buying another graphics tablet pen if you have lost it?

Answer 1

In short, no.

The graphics tablet pen is detected by the tablet itself because of something in the stylus - the most common method currently being Wacom's "penabled" technology. For this, a coil located in the pen interacts with the magnetic field produced by the tablet, producing a current to power the pen. This lets the pen - which has quite a bit of circuitry in it, actually - to communicate with the tablet. The tablet, in turn, has a grid of wires running across it which lets it detect the location of the pen according to the pen's own magnetic field.

So, really, there's an awful lot of technology in your pen, all of which is necessary to let it do what it does. There's a good reason for them being so expensive!