I gonna agree with lcummins on this...
Mac is very over priced for a buget, the machines you can build today with the parts it almost cost 3 times as much by just slapping Mac on front of it, painting it white and getting a cool sleek design but if you don't care about any of that, then -$2000 and get a PC, LOL.
As the old PC's to new PC's you can get by with 5-8 year old PC's as apposed to newer ones but it depends what your using it for, like e-mail, browsing, composing editors, programming, picture editing, etc.. older machines can be used for this but the newer graphics, anti-aliasing, HD avi, mpeg, xvid codecs rendering, DVD compression, GAMING, etc... a newer PC will benefit greatly in these areas..
I'm in the mist of building a PC myself this year.
My parts:
Intel Dual Core 2 https://compare.intel.com/pcc/showchart.aspx?mmID=35605&familyID=1&culture=en-US
Dual Core Duo Family https://compare.intel.com/pcc/default.aspx?familyID=1&culture=en-US
(more processors that are cheaper)
(There's also Intel® Core™2 Quad processor and Intel® Core™2 Extreme processor but to stick to budget Dual Core Duo should be just fine)
8 gigs of ram CORSAIR 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory - Retail (new egg has very cheap total cost $160+shipping)
https://www.newegg.com/Product/Product.aspx?Item=N82E16820145184
EVGA GeForce 9800 GX2 Video Card - FREE Crysis PC Game, SSC Edition, 1GB GDDR3, PCI Express 2.0, (Dual Link) Dual DVI, HDMI
https://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3830973&CatId=3669
Antec TruePower Quattro TPQ-1000 1000W ATX12V / EPS12V SLI Certified CrossFire Ready 80 PLUS Certified Active PFC Power Supply - Retail
https://www.newegg.com/Product/Product.aspx?Item=N82E16817371012
Power Supply, I'm using 1000W but with a heavy GPU card then you might need at least 500W or more
Hard Drive space at least 1 terabyte these days why not it's so cheap!
D-Link DGE-530T 10/ 20/ 100/ 200/ 1000/ 2000Mbps PCI Gigabit Desktop Adapter 1 x RJ45 - Retail Agreed with the
gigabyte network cards (NIC) these days like lcummins was saying, it used to be way expensive but transferring giganto files especially after rendering videos will make this less tedious!!!
https://www.newegg.com/Product/Product.aspx?Item=N82E16833127134
Depends on what OS (operating system) you going to get as well, mainly all you can find out there on retail shelves is Windows Vista and this DVD image of an OS is a memory hog, hence at least the 4 gigs of ram, Vista Ultimate supports 8+ and I think all the way up 128+ with servers but no need for that, LOL. (Of course this being the 64-bit version, you can dedicate a number of instances and different processes per CPU which is really nice)
Let me know if you have any questions and feel free to contact me by PM if yah want, I'm a software engineer and server designer by day...