first off you will maybe need to search online for best deals but basic setup requirements: MC does not use multi core so no point going for some ubber 8 core monster, a good 4core or even a high end dual core would be fine, but that said you may well want to use for gaming later on & this setup may be under powered.
ram & mother board: you should get the best you can afford & match the speed of ram to the MB no point having mega fast ram & a mb that runs 133 so, as win7 & over requre at least 2gb of ram to run them selves you are looking at having at least 4gb of ram more if you can afford.
hard drive: the search time is more important that the over all size of drive, a 520 1tb will be a bit slower than a 720 500gb, when the system is clean its not an issue but later as the disk gets fragmented it can be noticeable
graphic card again get the best you can afford any good budget card will do you, but remember that if you get a older version of one of the better card you need a good power supply with the correct power cables, my oldish 1gb ati needs 2 power inputs one for card one for fan.
my hand built box is a amd fx 4x 4.2gh with bundled fan, asus mb, sata hd 720 300gb, 1gb ati "under clocked coz of fan noise, older model" 8gb ram 800 watt ps with lots of out puts, case is a random case with front usb2-3 & mic/phones, aint great but runs D3/DW2 fine in high rez, cost me around 500 euros to build maybe a little over I forget but was well under 600 anyway, monitor is a good stable mid range samsung I had worth at least 200 so add that on top if ya like.
ps there is no way you can get a monitor worth having for that price so see if you can get an older one from a junked pc off friend or family for now & buy something better in the future.
the key is to research & visit any & all review sites related to each part to see if its really value for money & not junk your looking at, or research a ready made budget pc.