This is a very simple ignition coil driver circuit which can probably be built with stuff from your junk box. It is very easy to construct, and can be done in a few mintues. You need an ignition coil, a household lamp dimmer, and 1uF capacitor (600V for added safety).

This circuit should be good for about 10-20kV, depending on the ignition coil you use. Here is another very easy ignition coil circuit which runs from line voltage as well. It uses a TRIAC and a DIAC and can produce extremely high voltages (up to 40kV) from 120VAC input.

Higher voltages can be obtained by increasing the .1uF capacitor to .3uF or .4uF. Make sure the capacitor is below 1uF, if you do not the coil will probably be ruined.