I find it hard to believe that you would face tough legal consequences for something like this if the authorities ever found out. Maybe there would be something minor or maybe there would be threats for the future, but it seems to me that you would likely end up in a mental institution, at least for observation, and face healthcare related consequences rather than ending up in prison with the kind of a years long sentence a murder-for-hire suspect might get.
However, I also read somewhere, like others have already pointed out, that finding an assasssin for hire is next to impossible, so this option would likely be unsuccessful, anyway.
Besides, if you ever found yourself having enough money to hire a contract killer, then you would surely also have enough money to travel to another country or to use the Dark Web to get all kinds of substances with a much higher success rate.