Good 3D printer for ABS plastic enclosure for electronics, including threaded holes?

What does a heated bed do? Also, I've been reading about dual extruder, how does that help?

All valid points by jimc.

Take a look at http://www.thingiverse.com/thing:643264, an openSCAD version of the small project boxes you are talking about. Use of the "polyhole" approach by nophead helps control the hole diameters greatly; at least it has for me. Properly sized, I have found machine screws like M2, M3, #3, #4 can readily thread into holes without requiring the hole to be pretapped.

Here's an application where the inside of the box had standoffs added for board mounting http://www.thingiverse.com/thing:643351.

I'm no expert on openSCAD, nor saying that is the perfect answer. Just conveying that there are techniques out there that can accommodate what you want to do.

Would I do it on a professional basis? Probably not, at least not with PLA. The threaded holes do tend to wear and no longer hold the hardware.