Rural King has their house brand synthetic (I believe it is Citgo, but I'm not sure) on sale for $2.49 a quart. No MIR.
0W-20, 5W-20 and 5W-30 are all Dexos1 approved for those with GM cars under warranty.
Also available in 5 quart jugs in the same viscosities for $9.99 ($1.99 a quart).
2015 Chevrolet Impala
2008 Subaru Impreza STI
2004 Suzuki Hayabusa
1987 Honda VFR700F2
2011 Jonsered 2188 Chainsaw-The Judge.