Is there an idiom that refers to the money paid to get a killer to kill someone? I thought blood money was that expression, but it doesn't seem like there's an idiom that refers to it and blood money seems to be more general. I think dirty money refers to money that comes from any crime though.
A more general term we could consider is bounty.
A bounty is money that is offered as a reward for doing something, especially for finding or killing a particular person. A bounty of $50,000 was put on Dr. Alvarez's head.
The usual phrase is a price on his/her head, an amount of money that will be paid for the capture or death of the individual concerned.
There does not seem to be a specific word for the money paid in a contract killing (one in which a person hires an assassin or hitman) as distinct from a "bounty" (money which is offered for the capture or killing of a person by anyone, with no contract). You should not say "He offered a bounty of $1000 to the hitman to murder his wife."
In contracts generally, the money that is paid is called the "consideration". "money etc given to the party in exchange for contractual promises" If you are describing a highly professional killer, and want to use legal terms, perhaps in order to make it appear "respectable" you could say.
"He offered a consideration of $10,000 for the killing of his erstwhile business partner."
However, there is something ironic about using legal terminology to describe elements of an illegal agreement.
Otherwise simply "payment" or "money", or no word but implied through the mention of dollars etc.
The hitman was paid $1500 in advance and was promised a share of the $100 000 life insurance.
"Blood money" is money that a killer (but usually not a murderer) pays to the family of the victim, in some cultures.
If you hire someone to kill someone else, that person is called a hitman, and you have placed a “hit” on the intended victim. You can refer to the payment as hit money.
I guess technically you could say “hitwoman” if the person is female, but I have never heard of this situation occurring and don’t think I have ever heard this term actually used. It may have happened at some point, but I don’t remember any incidents of it.