To the OP: If you are so desperate to get MQMs that you're willing to fly in coach, consider seeing if you can adjust your trip to cover a Saturday night. For example depart home on Saturday night instead of (presumably) Sunday night for a workweek trip would be enough to do it. Or stay over the weekend after your trip and come back home on Sunday. Either of those may be enough to drop your fare substantially, and if you value the MQMs enough, you could consider covering a hotel stay for the extra night on your own dime if necessary.

Alternatively, if you are going to go for the buying Y route, you could also use miles to upgrade, especially since if the Y fare is $2-3K, presumably it is in a high enough Y fare bucket that the number of miles will come down somewhat.