Here's what I found:
mPerks coupon for 15% off any auto dept item less mPerks coupon for $7.00 off a jug of PP or $4.50 off a jug of QSUD and you're down to a little under five bucks a jug for either after their MIRs.
YMMV since mPerks doesn't always offer the same coupons to all users, although all three of these were available to both my wife and me in our respective accounts.
The 15% off is good only through Saturday 8/5.
If you can get the deal, this does make for some really cheap syn oil.