The heart turned out about 6.5x6.5 cm.
What you need:
A computer with CAD and CNC mill (Depending on the shape that you want to make and the material you choose to work with. If you are going to do some really simple shape you can manage without this)
1 Battery (C2032 3V)
1 Red 6mm LED
1 Tilt switch
2 Resistors (16 ohm)
2 M3 Bolts with nuts
2 pieces of 100x100x6 mm plexiglass
(optional) some heat-shrinking tube
This probably cost me around 20$-30$ but i bought enough parts to build at least 30 of them so building one will probably cost you around 5$-10$ since single parts are usually more expensive than packs of them. The two most expensive parts are the switch and the battery.
It does not take much experience but basic soldering skill and basic CAD knowledge will make it a lot easier.
I used http://led.linear1.org/led.wiz to find out which resistor to use.