Rangers defender Bates, 21, has struck a pre-contract agreement with Hamburg and will join the German club on a four-year deal in the summer.
The Gers were in talks to extend his contract but boss Graeme Murty claimed they were blown out of the water by Hamburg.
However, Commons believes Rangers should have been able to stump up the cash.
He said: “I can’t even begin to work out why David Bates has been allowed to walk out of the door at Ibrox to sign for Hamburg.
“The money that has been quoted in terms of his wage demands is not mega-bucks.
“If you consider the players they’ve brought in and the wages they threw at them when Pedro Caixinha was there, it’s just not unreasonable.
“If you can’t offer seven grand to a player who’s probably been your best centre-half this season, what on earth are they going to offer to someone else they are looking to sign?
“It’s crazy. As a young Scot growing up, if you support Celtic or Rangers, it’s your dream to play for those clubs and stay there for the rest of your career. Kieran Tierney would play for free for Celtic if he had to.
“For a club to be in a position where they can’t afford to give a player the minimum salary for an Old Firm player is waving the white flag.
“Rangers have made a habit of losing good Scottish players like Bates. Barrie McKay and Danny Wilson also walked out the door.
“These are Rangers fans, Scottish players who knew what it was all about. Boys you could build something around for the future.
“For a club like Rangers not to offer a guy like Bates seven grand a week is pathetic.”
Rangers suffered a humiliating 4-0 defeat to Old Firm rivals Celtic in the Scottish Cup semi-finals yesterday and Commons believes they need to spend big if they are to challenge the Bhoys’ dominance.
Writing in the Scottish Daily Mail, he said: “Before Sunday, I felt this Rangers team needed tens of millions thrown at it to have a chance of competing against Celtic. After seeing the performance, it could be £100m.
“If you brought in ten players on £15,000 to £20,000 a week for the next three years, including transfer fees, that could gobble up £70m. But that’s the kind of investment that’s now needed.
“They are so far behind their city rivals it’s incredible.”
