If you have to buy one prebuilt then
http://www.ibuypower.com/Store/Intel...5_Configurator isnt a bad idea.
change the gpu to a 7770 you have 5 hours left to get the presidents day sale deal
change the ram to 8gb if you can squeeze it
and lastly change the power supply to a 500 watt. That should put you at around 730 dollars. You will still need a monitor though.
You can browse their monitors and buy one, or buy one from somewhere else. If you want to go prebuilt your going to have to increase your budget to 900+ dollars if you want a monitor