I am hoping that I can use the printer to make parts for a business that I want to start.
the parts will need to be more durable then pretty. I think that the SD3 can get my foot in the door. Just a suitable starter model to get some prints under my belt.
I do like to tinker, and building an enclosure will not be a problem, dad and I built the house that they live in now

thanks again for the help!

Probably best to read up on all the differing printers out there and see just which type fits what you will be doing... home use/business/etc... I will bet there are more then a hundred manufacturers making under 2k$ printers now but as you look around there aren't more than 4 or 5 distinct types or printers each with their own pro's and con's.

I would guess a lot depends on your abilities....electronics, physics, tinkering, etc.... this will have a large effect on how much you will have to spend to do mods and such that may improve you printer.

As for the SD3 to SD4 difference the main thing is finish look... don't underestimate the worth of a finished look some people will spend 200K on building a house with 50-60K of that wrapped up in just kitchen finishings not much different when it comes to tools... homebuild look or pro finished look???? just depends on what you want to spend the monies for form or function...

Filament...... there are a few threads on here about filament and what works best for some people a quick search should show what you are looking for

I am looking at the SD3, why would I spend another $300 on the SD4? or other brand entirely?
-3D printing seems like the wild wild west at the moment. So many brands out there its hard to keep track. I got an SD2 recently and have been happy with it. Others will kill their first born child before buying a SD again. Experiences vary a lot. Sometimes its SD's fault for sending a faulty product....many times its the users fault for not knowing what they're getting into. If you're not a tinkerer, 3D printing is not ready for you yet.

How long should I expect it to take me to upgraded and get good prints?
-This just depends on how picky you are. Some people are happy out of the box with a few calibrations. It also depends on what your printing. If you printing just mechanical parts and don't need all the faces to look perfect it'll go quick. If you want to print detailed figurines and models it'll take more work.

I see filament form $20 to $40+, what am I getting for $20 more?
-Don't know. When I look through all the reviews for filaments it seems like a crap shoot. Don't know if $40 will get you a significantly better roll than $30. It does seem like the brands will get you a higher % of better rolls though. How you care for your rolls makes a difference though if you live in a high humidity region.

I have seen meany post about what people have done to upgrade their machines. 

What are the most important things to look for in a new (or used) printer?
What should I expect to pay for the upgrades?
I am looking at the SD3, why would I spend another $300 on the SD4? or other brand entirely?
How long should I expect it to take me to upgraded and get good prints? 
I see filament form $20 to $40+, what am I getting for $20 more?

ANY thing else that may be of use.

thanks for the help.
ZF