Sheldon Silver was the ultimate cheap date — bedding his “Barbie doll’’ mistress at budget hotels paid for with his taxpayer-funded per diem, sources told The Post on Monday.

“It was the worst-kept secret in politics. Shelly would stay at [cheap Albany hotels] when he was up there doing state business. She was seen leaving his room on a number of occasions,’’ a politically connected source said of the convicted ex-Assembly speaker and Janele Hyer-Spencer, one of the women with whom federal authorities say he had affairs.

“He got a per diem, a certain amount of money allotted to him for his travels,’’ the source said of the Manhattan Democrat.

“Let’s say it’s $100, and he spends $25 on accommodations and $25 on dining for the night. Then he’d pocket the rest. That’s why he chose’’ cheap hotels, such as the Red Carpet Inn, where rooms start as low as $55, the source said.

“He’s a penny-pincher. He’s a cheap date on someone else’s dime.”

Hyer-Spencer — a former assemblywoman known as the “Barbie doll’’ around Albany because of her blond ponytail and pretty face — and lobbyist Patricia Lynch were outed as the former speaker’s mistresses on Friday.

Both Hyer-Spencer, 51, and Lynch, 57, are married, as is Silver, 72. Through their lawyers, they’ve all denied the affairs.

The information will be considered by Manhattan federal Judge Valerie Caproni when Silver is sentenced May 3 for his $5 million kickback scheme.

The notorious skinflint Silver often romped at the Red Carpet Inn on Northern Boulevard, which boasts a view of the state Capitol’s rooftop — but little else.

“The walls are thin and you can hear everything — and I do mean everything,’’ a reviewer wrote on TripAdvisor Web site in August.

Another customer added, “Cheap — yes. Sketchy — oh yes.’’

Neither Silver nor his lawyers returned messages on Monday.

A woman who appeared to be Hyer-Spencer refused to answer the door or phone at her Staten Island home, and her lawyer did not return a message.

A spokesman for Lynch said, “Pat, she’s a tough lady. She’s back at work.”

Additional reporting by Carl Campanile, Larry Celona and Kevin Sheehan