Multiple extruders?

I want to upgrade my Mendel90 to multiple extruders at some point (using a RUMBA controller and stepstick drivers), both for the multi-color capabilities, and also the ability to extrude dissolvable support material like PVA.

First off, does anybody make a multi-extruder system that uses 3mm filament? I want to use that because that is what I am set up for and I would rather not have to keep more than one filament size around (also like the ability to use larger extruder nozzles).

Second, what multiple extruder systems are available besides the ones from E3D? I like my E3D-V6, but E3D tends to be a bit pricey. Are there any less expensive ones that work decently?

Third, do all multiple extruder systems have Bowden extruders, or are there direct-drive versions as well? I have no experience with Bowden extruders, so I don't know what to expect from them.

What about the new E3D lite6 ? It's not expensive.

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You don't necessarily need to buy a multi-extruder system. Those should be easier to incorporate (if the mounting is compatible with what you already have), lighter, and more compact, but you can find or design parts to adapt your X carriage to accommodate multiple single extruders, which would give you the flexibility to use one high-temperature extruder and one inexpensive extruder, or one direct drive and one bowden extruder, or one thermoplastic and one syringe extruder, or whatever strikes your fancy.

Multiple direct drive extruders would be heavy for a Mendel x-carriage and likely to impact the speeds and accelerations you can achieve, and you'd need to space them far enough apart to accommodate the drive motors, which could have a more signficant impact on build volume. Even a single direct-drive extruder could potentially affect speeds and accelerations, especially if you're hanging the hot ends for additional extruders off the x-carriage as well.

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Zavashier
What about the new E3D lite6 ? It's not expensive.

I want to be able to print hi-temp materials, though, not just PLA and ABS. That's why I bought an E3D-V6 in the first place.