This is a design I like primarily because it tends towards rigidity. And scaleablity (i.e. it is easily modified to increase build volume. Would use a Duet electronics board (or else something like a Pica) rather than a ramps. (Oh dual extruders would be nice).
One other thing to consider is that if you have a good moving cartesian system and you have made it rigid enough, one can change the “tool” (i.e.extruder) and substitute something else laser, router head, ink pin, scanner and have a multiple purpose machine that you can change the tool on and use for a different purpose. Not necessarily suggesting we do that initially but as a design goal, so we could do so later if desired.
http://www.instructables.com/id/Arduino-Controlled-CNC-3D-Printer/ illustrate this idea (not suggesting necessarily this as a candidate). Here is a commercial device which illustrates the idea (not suggesting this one because of cost).
Here's one on kickstarter http://www.snapmaker.com/kickstarter-lead.html
Its very interesting however the build volume is a little small. And they don't give details on the electronics module.
Agree that modular tooling around a Cartesian robot would be nice, but there are limited devices that support this. In any event, Kickstarter 3D printers are not an option; many of them go under before production starts, and we would not be guaranteed a machine.
As Brent has noticed the Ardunios (except perhaps the Due) are under CPU powered, something more is needed that is why the Duet is of interest to me. The Ramps board also has other problems so an improved ramps (rambo, pica) to me is the minimum.
Most commercial machines don't seem to be value for the money except for improved software. One disadvantage of a commercial machine unless they are of an open source design you are at their mercy for repairs, and upgrades.
Depends on the community. Some commercial designs (like Monoprice's) have a thriving modding community.
For the 3D printer, I would suggest the Monoprice Maker Select Plus 3D Printer ($399) or the Maker Select 3D Printer v2 ($318)
I'm hesitant to share my opinion since I'm not very involved and don't know what the interest is like for the thermoformer. I'm not totally up to date on the status of equipment at the space. So FWIW, it looks to me like thermoformers are very expensive for a limited use case, more useful to commercial production. In other words, how much would it really be used?
In contrast the 3D printer is a core technology, and the printers at the space previously were either very small or need committment and collaboration to have fully functional. The Mbot printer that was there is actually really decent mechanically other than a severely warped build platform. The support is not great, but if the controller has firmware available that is reliable and usable and supported by a usable software package it should do what most any printer you buy can do.
At the $500 point, there are not many good sizable 3D printers with heated bed and dual extruders. At the $900 point, you can now get a FlashForge Creator Pro (Makerbot clone). https://smile.amazon.com/FlashForge.../dp/B00I8NM6JO http://www.flashforge-usa.com/creator-pro/
I'm not the expert on software/firmware on these, in the past I just flashed Makerbot firmware and had the most success with their software. I spent my time printing and optimizing prints, not trying to get it to print. It looks like it probably can work with Sailfish but I haven't been able to confirm details.
I have several 3D printers in my classroom. They all were affordable or we could not have purchased them with the limited grant funds I could scrounge up. The following are what I have and know work well: Polar3d, M3d mini, Davinci duo 2.0 and a Davinci 1.0 All in one 3D printer Scanner. I do believe any of these with the exception of the M3d mini meets your requirements. I will say the M3d does a great job though but it's print size is small. Good Luck!