If you want an example of a real turnkey 3d printer that is useful, the Lulzbot TAZ 4 is a great machine (and currently retails for less than the Makerbot)
Yeah, but that's still a $2K printer, and that's my point.
People will it seems happily pay $2K for a 3D printer that really works. So it's easy to think that will pay at least the same for a PnP machine that really works.
As far as the $300 price goes, it's not as absurd as it sounds. That price would be for a barebones kit of parts, mostly sourced from China. You would be responsible for building it, wiring it, and printing your own feeders using the 3d print nozzle. The delta design uses considerable less parts and less motors than the Prusa i2 that I build for $250, and that wasn't sourced from China. I don't plan on making any profit from the cheap kits, I plan on making my profit from taking the same design, and selling a full-featured, fully-assembled commercial machine with a full set of feeders/nozzles, with support and warranty, for $5000 - $10000.
And you'll most likely make a killing,
if it works reliably.
A lot of people are already paying close to $5K for that Chinese one.
One potential problem I can see with the $300 DIY version, is that it's just that DIY, and people will, with absolute certainty, screw it up and it won't work right.
And well, ok, so be it, but the thing is that that could reflect badly upon your higher end fully built model if "word gets around" (even if it's not your fault) that the product has issues. Just something to be cautious of by trying to shoot for a low end low cost DIY model first.
The 2nd issues about shooting for a low target price for the base model is as I have mentioned before, having that in the back of your mind may ultimately cause a compromise in the design that turns out to be the Achilles heel for reliability or accuracy etc that unwittingly flows into your high end model.
e.g. you've chosen and presumably locked into the Delta design, and that looks great now, but what if it turns out to just not be viable right on the edges of performance where you need it and people expect a $5K machine to work at?
And even though I don't know much about this stuff, that's what my engineering spidey sense is telling me might possibly happen here. So personally I would likely have gone for pretty much what the Chinese design has, and then figure out ways to either tweak the cost, or add a killer feature etc.
But hey, I could be wrong, take with a grain of salt. I think what you are doing is great.