We'll assume that you have a computer.
The absolute minimum basics for audio post editing - we won't get into rerecording - are a DAW, an audio interface, audio monitors and some sound treatment. If you want to do any VO, ADR or Foley work you'll need to add a decent mic or two. I strongly suggest a video monitor.
For an ultra-low budget firewire audio interface I like the Focusrite Saffire Pro 14, around $250. There are several choices for passable low budget audio monitors - JBL LSR2325P ($400/pr), Tannoy Reveal 501a ($360/pr), Yamaha MSP3 ($300/pr). Not much volume or low end, but fairly clean and accurate for the price. You can get decent room treatment starting at $4.75 per square foot.
Your choice of DAW will depend upon whether you use a Mac or a PC. Pro Tools is cross-platform; bundled with the M-Box2 audio interface it's about $1,000. Other candidates:
Cubase Elements - Mac/PC - $100
Cubase - Mac/PC - $500
Adobe Audition - PC - $350 - Mac - $330
Digital Performer - Mac - $490
Nuendo - Mac/PC - $1,800
I'm rather curious as to what you thought audio post entailed. You seem completely ignorant of the process. Please don't take it as an insult; 99% of indie types are woefully ignorant of production and post sound. Why? I have no idea. Perhaps it's because you all are visually oriented and sound is "invisible." One of my favorite aphorisms is "Filmmaking is the art of the invisible; if anyone notices your work you haven't done your job right." In filmmaking obvious flaws pull you out of the illusion, so no one notices the good stuff. You watch a great movie, and perhaps you notice the score, but no one - except for other audio post guys and gals - say "WOW!!! What a great sounding movie!"
So you may want to rethink your priorities and let someone else handle your audio post.
Your film will only look as good as it sounds, because
"Sound is half of the experience."