I have a vehicle that requires synthetic oil, and I change it myself. 5 quarts of full synthetic is roughly $25. Conventional about $15. That will cost me about an extra $100 every 100K miles. Its worth it to me. Sure, conventional oil has been used for a while, and its probably fine for most older vehicles, I wouldn't use anything but synthetic in a newer car. Again, it is start up conditions where the synthetics are far superior.