If you're budget conscious, Ebay is your best bet. The search I set up there will find anything with:
100GB+ HD space (The games you listed won't fill it, so you're good to go)
Windows XP/Vista/7 or Unspecified/Not included operating system. If you have a computer you're replacing that has a current windows license, borrow an OEM disc from someone and use that code to put it onto the other computer. If you have issues Windows isn't that much comparitively.
No graphics card was specified. You can get a decent NVidia card for less than $50 at Best Buy. I ran on that card for years and it ran WoW/Fear/The Witcher and just about everything fine. I also played Mass Effect 2 and a lot of newer games on it as well.
At least a dual core processor or better. Some games like ME2 physically require a multithreaded processor to function. It was the only reason I moved from my overclocked 3ghz single core into the quad core range.
DVD drives and everything else can be easily added later.
Your next best option is to find out what the best processor your current motherboard can handle is, and grab it off of Ebay. Then get a decent mid-range video card like what I mentioned before. Grab a 450+ watt power supply. I recommend just splurging here so that you're ready for future upgrades. I bought a 450 and ended up having to move up to a 600 a few months later for a new graphic card. Then determine the best and fastest RAM your motherboard can handle and get what it'll take. Pay attention to dual channel. It's better to have matching 1GB sticks for 2GB dual channel paired than a 1 and 2 set that can't be accessed as quickly. Lastly, get a case that has lots of room for future upgrades and has some good air flow. A case that is pre-configured for optional liquid cooling would be good.
Once you're set up on that end, every time you have a bit of cash you can toss new parts in. Motherboard/CPU bundles are fairly cheap, and you can get them with more RAM nowadays too.
This is the method I took personally. My chain of computer progression started with an IBM 8088 with 640KB RAM, DOS 5.0, and a 10MB hard drive. 16 color VGA output and I was rocking QBasic, ZZT, and Oregon Trail.
Now I'm running a 2.3 GHZ quad core, ATI Radeon HD 5850, only 2GB DDR2/800, but I'll be moving up to 4x 1GB 1066 pieces soon, and 80/150/320GB hard drives. (Operating System/Programs/Storage setup).
Before committing on EBay, if you choose that route, definately research each piece of the machine to make sure you're not getting a recalled motherboard or something that's not compatible with something else. IE an Intel board with NVidia chipset that someone claims to have set up ATI Crossfire on, or SATA drives on an IDE only board.
Price isn't everything. I use the reviews on NewEgg to check out any part that is currently on the market. If it has poor reviews, I don't touch it.
And Craigslist is an invaluable source. People may put computers up in the free section saying "Free if you want it for parts". I'm actually typing this on a Satellite L505 that is just now reaching a year and a half old. A girls dad got mad and threw it against the wall while it was on. Trashed the hard drive. I took it for "Parts". Everything else was fine - The top doesn't align perfectly when it shuts, and some of the side doesn't snap together right, but it's never crashed on me since installing a new hard drive and reseating the cables and RAM. I have several laptops I've received the same way. In fact, all my computers except for a netbook I purchased for business use started as freebies that I replaced a few parts in to get started. Even my gaming machine.