Seems like you have to check all of them, if you want the best price. I just discovered partsgeek last night. Seems like their pricing is similar to rockauto. I also check ebay and amazon too. Then there's 4wheelparts.com, and engnbldr.com and a few other more specialty places like
Marlin Crawler, Inc. | Originator of Rock Crawling (since 1994) and the like. Plus I always check out the local big places like autozone, pepboys and advanced. We don't really have a "local" store here. When I lived in Raleigh, NC I used to go to this place called Loop Road. It was awesome. Always the same guys behind the counter for years.