I’m there with that. Happened to me once. Boss told me he wanted to promote me, and that he felt I could be taking on more responsibility. Naturally, I asked about the changes in compensation and benefits.
He looked at me like I’d peed on his foot, and explained that there would be ‘changes’ in my compensation package. I asked what they would be. He did not want to talk about that, he wanted to talk about my new responsibilities. I explained that I had not yet accepted the position, and that I would not until I felt that I understood the whole picture.
He looked at me like I’d peed on his OTHER foot, and explained the package.
In which I found myself in the OP’s position, and respectfully declined the promotion. He asked why. I told him “because I cannot afford to lose the overtime and side perks, they being necessary to my household budget.”
“Oh, so you feel that you can’t handle the added responsibility?” he asked.
“No, I cannot afford to lose the overtime and side perks, they being necessary to my household budget.”
“So you don’t feel that you’re up to the job?”
“No, I cannot afford to lose the overtime and side perks, they being necessary to my household budget.”
“I don’t understand your resistance to a higher position in the company.”
“I. Can’t. Afford. A. Pay. Cut.”
“But this position is a move UP, and looks great on a resume! How can you turn it DOWN?”
Wound up transferring to another department.
I sincerely hope the OP’s management is better and more understanding than mine was.