You never did say what you want to do with your computer.
For $500 or less, you will have a pre-built computer that will be good for e-mail, word processing, older games (at least 6 months old) and other small projects.
Now, that said, be sure to ask the manufacturer which mobo they use. This is important if you want to future proof (upgrade) your computer. If they use a mobo that will only use one processor, then you are stuck.
I had this happen to me and I spent about $2000. I bought from HP and got the top of the line. However, they used a mobo that would only accept an AMD Athlon 1.4GHz. So, when I decided to upgrade to a new processor---no can do.
The motherboard is not one of those items that they like to divulge to purchasers.
I would suggest HP. Go to this link:
This is HP's forum. You can get some suggestions from its members about a good computer in your price range. They are very helpful.
Remember that you will have to pay shipping.