The Texas Rangers are only two games behind the Red Sox in the Wild Card race. I doubt either team will sell off.
Because the of luxury tax, the Red Sox probably face more financial constraint than the Rangers do. According to Cot's Baseball Contracts, the Rangers have only $93 million (including Adrian Beltre's $18 million) committed to the 2018 payroll after opening this season with a $165 million payroll:
Meanwhile, the Red Sox already have $123 million committed to the 2018 payroll after opening this season with a $197 million payroll:
Texas does not have a small-market team looking to shed payroll. With the nation's fifth-largest television, the Rangers rank 11th with a team valuation of $1.55 billion, according to Forbes magazine:
https://www.forbes.com/pictures/58cc474f31358e1a35ad373d/11-texas-rangers/#112282b164c6
The Red Sox rank third in team valuation at $2.7 billion, albeit with slower one-year growth than the Rangers:
https://www.forbes.com/pictures/58cc474f31358e1a35ad373d/3-boston-red-sox/#7c1449077275
I doubt the Rangers would trade Beltre for anyone short of Rafael Devers ... and even Devers might not be enough.