A few watt diode will cut plastic depending on the colour of the plastic of course!!!!

2.4 watt IR should do the trick if 2mm Black plastic, Wont be fast though approx 200mm per min.

Have done it my self, wasn't difficult to set up laser cost about £100 from US ebay, Really easy to drive not like RF excited tubes or smaller diodes. I used an ATX PSU with a current limiting resistor.

Here is a pic of diode mounted onto an old Pentium 2 heat sink, The IR output is delivered by fiber optics to a colimator lens, So nice and easy to implement on Gantry router.




Mike.