This pretty much sums it up. The printers themselves are not that expensive, but the media (plastics) can add up quick. The nozzles will clog, and you will have lots of waste in the beginning. The whole technology is getting better every day, so it wont be long before everyone has one of these...
Its been possible to print them for a few years now. Its just they wont hold up very long. They have gotten better. They real nice thing is you can print your own High cap mags if they are ever banned.
PSA has some sales
http://palmettostatearmory.com/index.php/catalog/product/view/id/11791/s/magpul-pmag-m3-mag557-5-pack/?utm_source=Weekend+Deals+12%2F14&utm_campaign=Constant+Contact&utm_medium=email
http://palmettostatearmory.com/index.php/featured/dh-5-56-30rd-aluminum-mag.html