Synthetic oil is easy to get cheap. Advance and AutoZone regularly run sales, and even BOGO (By One, Get One). Don't pay full price for it; wait until it goes on sale and stock up.
Why, right now, you can get 5 quarts of Castrol Syntec and a Fram TG for $25:
http://www.autozone.com/images/in_ou...g4_0306_08.pdf
And keep an eye on the sales and promotions forum on BobIsTheOilGuy.com (BITOG):
http://www.bobistheoilguy.com/forums...=33&page=1
For example, it appears that next month, AutoZone is running Valvoline SynPower and a Fram TG for $19.99.