The only Indian gaming that existed in 1983 was bingo. That was five years before the Indian Gaming Regulatory Act passed. So I doubt the Pequots had much money to lobby Congress with, and casino developers had no reason to help them.
So they got recognition from Congress, but they didn't buy it. In fact, Congress recognized them to settle their land claims, not to pay them off for anything. Your mistake if you think otherwise.
Here, educate yourself about the Pequots' recognition:
Mashantucket Pequot Tribe
With the assistance of the Native American Rights Fund and the Indian Rights Association, the Tribe filed suit in 1976 against neighboring landowners to recover land that had been sold by the State of Connecticut in 1856. Seven years later the Pequots reached a settlement with the landowners, who agreed that the 1856 sale was illegal, and who joined the Tribe in seeking the state government's support. The state responded, and the Connecticut Legislature unanimously passed legislation to petition the federal government to grant tribal recognition to the Mashantucket Pequots and settle the claim. With help from the Connecticut delegation, the Mashantucket Pequot Indian Land Claims Settlement Act was enacted by the U.S. Congress and signed by President Reagan on Oct. 18, 1983.
Below: A reveler at a Foxwoods party? No, a traditional Pequot Indian.