Virgin America Elevate - what's MCS instant upgrade?

I'm looking at some fares from SFO To IAD and see that the MCS instant upgrade is only about 150 more than MC but at the same time I also see that MCS is much higher. What does all this mean?

If you click on the little "i" under each fare classification, it explains what is included in the fare class. For instant upgrade to MCS, the main difference is that for changes/cancelations, the cost is $75, the fare is refundable only in credits to your travel bank, and it is not transferable. Otherwise, all the benefits of Main Cabin Select are the same.