One Song (Mastering)

I need to do a mastering for my new single of about 4 minutes. The musical genre is Synth/Pop style. I would like to publish on the main online stores I would like to know the timing and the price. Thank you

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