From the perspective of Texas Tech and Oklahoma State, this would be a very bad idea. (my opinion)
Firstly, the SEC wouldn't permit either of those schools (or, any other school) to simply buy their way into the SEC . . . no matter what was offered.
Secondly, offering to take only a 20% payment would make Texas Tech and Oklahoma State look like beggars and chumps.
Texas Tech should be looking at getting into the PAC-12 or B1G, and Oklahoma State should be looking at getting into the B1G or ACC.
100% agree that any current Big 12 school who can get in to the ACC, Big 10, or Pac-12 should do it ASAP with no regrets. But it was already a pretty big longshot for any of them, and if those 3 conferences are responding to the SEC by aligning rather than by adding schools of their own, it's pretty much impossible.
The only schools that meet the academic standards of any of those conferences are Kansas and Iowa State, who are from small markets. Yes, any of those 3 conferences might bend their academic standards for a football powerhouse, but none of the remaining schools are. While there's a faint hope that the Big 10 could look at Kansas one day, or the ACC at West Virginia, in all likelihood those 8 Big 12 schools are stuck in a suddenly mid-major conference whose TV deal will be a fraction of the SEC TV deal.
Their best remaining bet is to scheme and plead with the SEC to go past 16, which I think is also unlikely but faintly possible. The SEC is going to want to gobble up ACC teams if we go past 16, but if this alliance is for real and holds together, who knows? Maybe schools like Kansas, Oklahoma State, and Texas Tech get a look, especially if they're willing to debase themselves to sweeten the pot.