First I'll start by saying that I do not work for, endorse, or get kick backs from RockAuto.com for writing this. Just spreading some money saving tips I've come across servicing my own personal vehicles!
I usually start looking at promos/sales from the usual chain auto parts stores like Oriley's, AutoZone, Advance, etc. a few days or weeks before I plan on doing preventative maintenance on one or a few of our cars. I try and group services together to save time and work if I know a few will be due around the same time or if I will have a certain part of the car off already.
Never heard of RockAuto.com? Essentially they're an online parts business based in Madison Wisconsin with warehouses in a variety of areas. What I have found to be different about them is they usually have a larger selection, and at times better pricing than what you can get from running down to the parts store down the street. Typically when you run down the street you'll get the "good, better, best" options but at times not even that. If you search for front brake pads for a 1990 Mazda Miata on RockAuto.com, you'll get 20+ options ranging from $4.95 - $34.79 depending on the performance level you're looking for. If that's the only thing you're shopping for it may just make sense to run down the street and pick them up when you factor in shipping and wait time if you're in a bind but there is definitely cost savings to be found if you're looking for a variety of parts.
Ok, here's how to do it. Jump on RockAuto.com and select the make, year, and model of your vehicle. Then you' click on the orange RSS feed logo.
At this point you can either sign up for notifications as new parts for your car are added to their catalog, or be notified of clearance items by clicking on the same orange RSS feed logo. If you just want to see the clearance items, just click on the HTML logo.
Here are the goods! Do some price checking and you'll see that while some parts are in line with other retailers, others have a pretty significant savings. Check out the FRAM CA6828 air filter. As of 12-11-15 it's available at AutoZone for $13.49 vs $3.44