The Supreme Court's widely derided ruling last week on presidential immunity opens up an extreme possibility — imagine a kiosk in the lobby of the White House where the president's "lap dogs" order get-out-of-jail free cards rather than fries and a soda.That's the country's new reality, according ...
The president’s power to pardon federal crimes is not really limited in the constitution except to exclude cases of impeachment. That is generally accepted to mean that the power of the pardon is otherwise nearly unlimited except perhaps that one cannot pardon oneself. There is no specific rule or law against giving a pardon in exchange for payment, though it is clearly considered by most as unethical.
Yes there is: 18 USC § 201 (b) (2).
Granting the pardon isn’t the part that’s illegal; soliciting or receiving the payment in exchange is.