I don't see why this is so hard. Every team in the division has a good interior line. The Eagles have Cox and Jernigan (who was a free agent). The Giants have a rookie they drafted, Dexter Lawrence, who looks like the real deal, and Dalvin Tomlinson who is a space eater. Then they traded for Leonard Williams. The Commanders have Allen and Payne. Look around the league. Almost every good team has at l east one really quality DT. The Cowboys have a couple of Jags starting.
This is the result of the Cowboys ignoring the problem for years. Remember when the offensive line was terrible and they signed a couple of Jags in the offseason? Nate Livings and McKenzie Bernadeau? What they paid for those two they could have pooled and gotten one quality OG. When it go so bad it could not be ignored they changed their philosophy and started using 1st round draft picks to fill the position. If they are unwilling to sign top free agents at that position, then they will have to get a high draft pick and draft one.