As you have a focus of polycarbonate, you are starting off on a good foundation. You'd want to find a machine with an enclosure as part of the construction, not an add-on, as it will also include cooling management for the power sources and also include provision for mounting the spools inside the enclosure. For nylons, which are astonishingly hygroscopic, it's a necessity. I don't know how PC falls into the moisture concerns. Additionally, the extruding temperatures are going to be on the high side and a printer advertised as being able to handle PC will have a hot end of sufficient capacity to manage those higher temperatures. I was surprised to see a 3D printer at a past area home show. It was clearly aimed at the industrial component of the world. The ad copy on the table was devoted to polycarbonate materials and other high temperature materials. The printer was "low-priced" according to the sales person, starting at US$5000. I'm a fan of the Prusa line of printers and their software, but for your purposes, it would be extending some good printers to the outer reaches of capabilities and possibly outside of those capabilities.