Was perseus rewarded for killing Medusa?

Indirectly. You see, he was given the task by Polydectes, King of Seriphos, with the intention that the Gorgon would kill him, and then Polydectes could have his way with Perseus' mother, Danae. But he was able to kill Medusa, and in turn was able to save Andromeda from the Cetus, slew her intended huband, then returned to Seriphos where he slew Polydectes and saved his mother. He made his foster father Dictys king and he made Danae his queen. Later, he returned to Argos where he fulfilled the prophecy that he would kill his grandfather, Acrisius, making himself king of Argos.