A JAA flight instructor rating requires a minimum of 30 hours of flight time. The courses usually cost at least €7000, depending where you go. Things are different in Europe than FAA land. Plus, plane rental is much more expensive in Europe than the US. In my local area, a Cessna 172 goes for €140 per hour. A DA-20 goes for €170 per hour, and a Seneca is over €400 per hour. Plus, the Flight Instructor course requires 125 hours of theory.
For what it is worth though, flight instructing is NOT voluntary (aka charity work). I have a friend getting paid €27/hr (continental Europe), another one getting 20GBP/hr (UK), and several getting €18/hr in a southern European country. I get the impression that lots of guys in Europe don't want to be an instructor and go straight to a jet. Of course this isn't everybody. There are other guys who resort to instructing because they couldn't get an airline/jet job. This is quite a different mentality than the US where a large majority start out instructing without giving it a second thought.