>>7807
Xeons are cheapest processors available. you can buy cheap ones for few $
price if 3.2ghz quad core for less than 30$
Mainboard is another 30-50$ depending on where you get it
if you buy server motherboard you will get ability to use shitload of super cheap and very reliable ram and you can even stick 2 processors making your system very powerfull.
If you just use common motherboard ram will be more expensive and you will be limited to 1 cpu.

If you only have laptop you are screwed.

if you want to go into 3d rendering for low cost I would recommend you to buy some crap computer with lga775 motherboard and 4 ram sockets then buy some XEON cpu from ebay and get 4 sticks of 2gb ram.

You do not need Nvidia card for Iray if runs pretty well on cpu too.
but if you have problems with iray you can try "lux renderer" or "reality", but those require more complex scene setup.