Litecoin mining rig?

Hey all,

I recently decided that I want to get into mining litecoins. I want to custom build a PC to leave running 24/7, mining. I'm pretty knowledgeable when it comes to software and assembling hardware, but when it comes to choosing motherboards and stuff like that, my mind blows. Basically I'm looking for an entry-level miner for absolutely no more than $500. I'm not concerned about power or anything like that and I'm not even looking to fully pay off the machine. I have a monitor and keyboard, and I plan to use Linux.

P.S.

Yes, I am aware of the risks of mining litecoins.

Tl;dr:

Litecoin mining rig for no more than $500