Oh boy, you asked for oil recommendations. Get ready for 20 different answers. I won't add to the long list.
Best site for cheap parts (including some OEM parts like from DENSO, NGK, and Aisin) is Rockauto:
2000 TOYOTA 4RUNNER 3.4L V6 Parts | RockAuto. I linked to your specific year. They also sell body and suspension parts, along with odds and ends like wire connectors. They are a forum sponsor as well and offer a 5% off code year round, just find them in the sponsor section of our forum and look for the most recent code.
McGeorge Toyota is the cheapest online US based Toyota dealer like mentioned by others. Use them for parts that you can't compromise on like the before mentioned lower ball joints. Actually, that applies to all steering parts really.
If you are short on money but have plenty of time, PartSouq has a warehouse overseas in UAE that ships OEM parts. I can confirm that they are genuine Toyota parts as I've used them before:
PartSouq Auto Parts Around the World. You just need your frame code and VIN to verify the correct parts. It can also help to look up the Toyota part number on McGeorge and then copy it into PartSouq to compare pricing. Some parts like sensors and more complex assemblies are offered at a deep discount.
If you plan on doing a timing belt in the near future, many of us use the Ebay seller aircabinman. His company sources OEM parts and offers them at discounts compared to dealer prices. Plus saves you from having to piece together all the parts. He sells a minimal kits with just belts and water pump:
V6 3.4 TIMING BELT KIT & WATER PUMP Genuine & OE Manufacture Parts! | eBay or the whole kit and caboodle to replace everything, plus a few other common parts that fail:
Timing Belt Kit for Tundra 4Runner Tacoma T100 Belts Rollers Seals PCV | eBay.
