I would like to buy hard drives for backups, but for cheaper than buying new at best buy or fry's electronics? Where can I buy hard drives?

Fry's and Best Buy are not bad if you can find one on sale. Years ago I got lucky and I got a 1tb WD Black Hard Drive that was on sale at Best Buy when I was in a pinch. Fry's will pricematch the sites you're looking for like newegg.com, amazon.com, bhphotovideo.com so frys is moot.

Although both Fry's and Best Buy are terrible about keeping things in stock. The only other big box retailer you can look at is Microcenter but since you didn't mention them, then I assume there is not one close to you.

Protip, pay extra to have the Hard Drive shipped by FedEx. UPS throws packages around and OnTrack is even worse.

http://www.pricewatch.com/

eBay

On eBay cheap

Walmart, or Best Buy.

Craigslist and ebay are the best places. Mercari has been useful in the past as well

Staples has some good deals on hard drives and memory cards, but not always. Microcenter is always near the best deal. Amazon is usually a good price. The problem with Walmart and similar is that they don't move these things fast enough to keep up with falling prices. They still want the full price long after the market has moved to larger drives for the same price.