If you are looking to build a computer on the cheap side of things, and you already have a monitor (I know you said you have a mac, but monitors are very cheap now so you can get one from pretty much anywhere) this is what I would suggest (mind you this doesn't come with any case fans so you will have to tac on about ~20 bucks extra for those):
http://www.newegg.com/Product/ComboD...t=Combo.500536 181.98
http://www.newegg.com/Product/Produc...82E16811146059 39.99
http://www.newegg.com/Product/Produc...82E16820227582 75.99
http://www.newegg.com/Product/Produc...82E16814130572 129.99
http://www.newegg.com/Product/Produc...82E16817153106 119.99
Now the thing that TMcMahon51 said about the cheap comp from the link, is true, that that AMD processor is pretty anemic, but you have to be very careful about the i7 in the 1366 socket form, as they can get much more expensive than a comparable AMD processor. As far as performance they are about the same, but the intel chips are much more compatible software wise (drivers and such with windows). Just thought that I would put my 2 coppers in on this.