The Heroes for Hire concept originated with Luke Cage's solo series titled Luke Cage, Hero for Hire.

As a "hero for hire", Cage tried to merge the usually pro bono world of
superheroics with the bill-paying practicality of private investigation.
Although the title changed to Luke Cage, Power Man in issue #17,
Cage continued with his for-hire activities.
Eventually he joined forces with Daniel Rand-K’ai.

Colleen Wing and Misty Knight often appeared with Power Man and Iron Fist.

Nowadays, Heroes for Hire is a group of (mostly) superpowered
mercenaries who hire out their aid in exchange for money.