One way that Lisa and I have been able to keep costs down as I transition to a home-based business is for me to do at least some of the auto repairs. Actually, that's probably been the case for well before I changed jobs, but now it's just more imperative that I get it right when I make a repair, unlike when the students at my former school put a new starter on my Suburban using only two bolts instead of three, destroying my vehicle and costing me thousands. (Can't have the ineptitude of MFHS Auto Shop in my driveway.)
When I need auto parts, I normally shop online first. You can get several prices and opinions online, and you can sometimes use a coupon and pick an item up in the store. Either way, it's good to know the part is at your local store, and it makes shopping easier to simply show up with a receipt or your smart phone.
I like Rock Auto for a lot of parts, and it's often the best price. However, I also like Advance for items I want to see before I buy or need today. I'm always taking my battery in for a test and I'm usually satisfied with my purchases from Advance. They've even been pretty good a couple of times with warranty issues on items (starter and battery). The fact that it's a local store should mean something to you for some of those items.
However, I think the local store wanted more than double what I paid for my replacement SAAB 9-5 radiator, so I had to find that at a special radiator shop. That said, I've found competitive prices on items for the following vehicles at Advance: Bertone X 1/9. Chevy Cavalier, Chevy Cobalt, Chevy Suburban, Chevy Malibu Maxx, and Lincoln MKZ. Unfortunately, I still have air filters I pre-bought before Lisa totaled her Malibu. Actually, that's some good advice: don't pre-buy too much for your car if you tend to drive it a lot or if you'd use it as a trade to get your wife a safer vehicle.