Is it illegal to offer money in exchange for parental rights? This has recently happened and it would seem that if selling a child is illegal that this would be too... But I can't find anywhere that addresses this.

If can differ as to who is making the offer, all one person can do is sign away ( with courts permission) their rights, they can not give the rights to someone else, only the court can appopint someone.

So if the person is the other parent also with rights, this is a custody situation, and payment in lieu of contractual rights can be a legal contract agreement.

I would consider it a bribe to get someone out of the child's life.