You know, I've looked at any number of PCs over the years and the one thing that I've come to the conclusion on is this:
If you don't spend at least enough for a midline PC or laptop, you will be pretty unhappy in the long run.
I would STRONGLY recommend that you spend a bit more to get a PC which has a decent build quality and doesn't fall into the middle of the road cheapest on the block variety, which there are plenty of, but all are of pretty low/cheap quality off the line in China.
I've used both expensive and cheap laptops - and the cheap ones didn't survive, while the expensive ones have not failed.
My $1,000+ desktop from 5 years ago we replaced last year with a $400 model. I will NOT use that desktop anymore and went back to my 5 year old model because it is simply a better product.
I think all manufacturers make good and cheap product, but at the end of the day, a cheap laptop just won't hold up for you long term.
As is typically the case - Best Buy isn't going to really offer much in the way of deals for you and you will be spending a bit more than you need to compared to buying directly from Dell or going to a place like Microcenter.
With the options out there, you want to consider that you probably want a current generation Intel/AMD processor of good speed, sitting on a good motherboards. RAM is cheap now, so memory is easy. Yet, a slow processor can't be overcome, so make sure that it is good.
If I had to go to BB and buy at $500, this is what I would get...
http://www.bestbuy.com/site/Dell+-+Inspiron+Laptop+with+Intel®+Pentium®+Processor+-+Pacific+Blue/9528825.p?id=1218119756637&skuId=9528825
If I was just going to buy a laptop I would shoot to keep it closer to $1,000 and would likely be looking here...
http://configure.us.dell.com/dellstore/config.aspx?oc=dndwda3&c=us&l=en&s=dhs&cs=19&kc=laptop-inspiron-17
Actually, I would likely go through the Dell Outlet store which can save you $200 or so off of 'new' pricing.
Yet, if this is for your home, and you intend to leave it installed at your home, the best value still is going to come from getting a desktop PC - especially if you are on a limited budget for this operation.
There's a LOT of compromise when spending $500 on a computer, just as there would be on an A/V system for that much money.