Top of the game: ProTools 10. Should go for about 700 USD if I'm not mistaken. This is a hollywood-level solution.
But you can do wonders with Adobe Audition CS6 or Nuendo 5.5 as well, which are about half that price.
Uh... Nuendo is a great deal more than $700. You can usually pick that up for about $1,700 or so but it's MSRP is around $2,400. http://www.sweetwate...detail/Nuendo5/ Perhaps you're mistaking Pro Tools HD versions, which can go up to $20K depending on the card set up you use.
Have you done sound editing before? I'm just asking because it seems like you are about to go on this task yourself and sound design is a very specific area and requires a lot of skill and experience.
Agreed! It sounds like you've either never done audio production or had very limited experience in it. I'm all for folks learning new skills but if you're looking for high quality audio for good bang for the buck (and at a faster turn around) then I'd highly suggest two options:
1) Hire a sound guy on here. Odds are you'll find someone who would cost about the same as it would cost you to purchase the software and the gear to record your source files (if you're making these from scratch).
2) Purchase royalty free sound effects from sites like http://www.soundrangers.com/ or http://www.sounddogs.com/.
You could even do both and have someone more experienced in audio do the complex sounds while you handle the simple sounds (like a button UI click) via the a la carte method. Of course if you're looking to create a game 100% by yourself, then that's understandable (and admirable). It really depends on what your goals and intentions are with this project.
Hope that helps!