how much does it cost to have a song mastered

how much will it cost me to have 1 song mastered. We have one song professionally mixed here on soundbetter and is ready to be mastered. thanks

Additional info:
The song is mixed and ready to be mastered. I don't have a hard deadline for this. I'm looking to hire a top pro who's worked on hit songs, and have the budget for that. I'm looking to master one song.