Fused deposition printing is still in its infancy. It's no where near "plug and play". You can get some pretty successful prints with cheap systems but it's touch and go weather your designed part will print right or not. If you have a printer to print parts that you design yourself you will find you learn quirks of your printer and design around them. It is a lot of fiddling working out what software/firmware to use with your setup. And then you get into different options in your gcode generator such as infill, support, etc. It is not for the light hearted. And it is not for someone who does not understand programming or electronics and electricity.
Saying all that, you don't have to be a programmer, or an electrician. But having a basic understanding of programming logic is pretty essential. And knowing how electricity flows and reacts through components such as resistors, capacitors, inductors, transistors and FET's is pretty useful to avoid many hours spent aimlessly trouble shooting.
I built a Prusa i1. I bought a plastic printed parts kit online. I bought experimental Gen 7 electronics from the maker in Denmark. I bought Nema 17 steppers from ebay along with the Pololu/Stepsticks stepper drivers. I bought the heated bed from ebay also (most of this stuff came from overseas). All my hardware came from either SmallParts.com.au or Coventry Fasteners.
All up I spent around the $680 mark and I did it on the cheap! That was at the beginning of last year, so prices have dropped. You can now build a Prusa i2 for around $500 I have heard...
There are three filaments you can use at the moment off the shelf. PLA (poly lactic acid) which is made from sugar using a catalyst. ABS and Nylon.
ABS requires a heated bed and warps a lot of anything larger than around 80 x 80mm (but completely depends on model design and dimensions such as thickness, solidness and height).
Nylon is a new option. It can print on non heated bed (best in a glued down fabric I have seen). It comes out flexible like you would expect.
PLA is hard and brittle but needs much lower temps for both the built platform and print head. It is also biodegradable and will lose form in hot temps around the 70c mark.
I don't see a point in a FDM (fused deposition modeling) printer with a bed size over 250mm x 250mm. Warpage even with PLA is too excessive for sizes over that size.
Going cheap on parts has caused me many headaches. Mostly with the electronics. I bought cheap stepper drivers and wish I just spent twice the amount on the proper branded Pololu's. Also going with the Gen 7 meant I had a hard time moving over from Teacup firmware to Marlin firmware.
I wanted to use Marlin because it had what they call "look ahead" which basically makes it so the printer doesn't have to decelerate to a stop at every change of direction; this stopping and starting happens so fast you can't see it, but around corners it is enough time for the print head to bleed a little and cause over sized edges.
To give you an idea of the electrical knowledge needed to change the firmware from Teacup to Marlin I had to change an inductor, cut circuit tracks and run new wires to create alternative paths for the temp sensors power.
To sum up my printer.
I have a Prusa i1
Gen 7 v1.3 modded to v1.4.1
Marlin firmware
Using Slic3r and Printrun on Windows 7
J-head Mk 5b print head mounted on a Gregs extruder
Nema 17 steppers and GT2 belts
Metric M8 frame with stainless steel Z axis rods
Have a look at my thingiverse profile to see some of the things I have designed and printed, and things I have downloaded and printed.
http://www.thingiverse.com/Phizinza/designs