Boyd left Rangers for Middlesbrough after his contract with the Scottish side expired last summer.
Rangers are looking to bring in a new striker following Kenny Miller’s move to Bursaspor last week.
“It’s a simple one, that one,” he said.
“We couldn’t afford to pay the money that Middlesbrough were paying last season and we are still in that position where we can’t afford to pay it now.
“It’s just a situation where Kris left us to go to a club who could pay him more money.
“We couldn’t pay him that money and we still can’t, and that’s the situation.”
