I don't spend any money on film audio, because I don't make films. Like APE (Audio Post Expert) I'm one of the people you want to pay to work on the audio of your film; APE works on projects with real budgets, and my niche is low/no/mini/micro budget indie films.
Sound-for-picture is a complex topic. As I have posted innumerable times:
Your project will only look as good as it sounds, because
"Sound is half of the experience."
This is not a mere platitude. By far the most common
technical reason a project fails is poor audio. So you must begin thinking about sound-for-picture during preproduction while you are working on your shooting script. The optimum choice for good production sound is to hire an experienced professional. Barring that you look for an up-and-comer who has a basic prosumer kit, a bit of experience and a lot of ambition. If you can't find that person you'll have to take care of it yourself, either renting or buying gear and "swinging" the boom yourself or having a PA/friend do the boom-op job.
Every dollar/minute you spend on production sound will save you ten minutes/dollars in audio post.
You may want to start with "The Location Sound Bible" by Ric Viers.
http://www.amazon.com/The-Location-Sound-Bible-Professional/dp/1615931201
So on to audio post. There are five elements to audio post - dialog editing, Foley, sound effects, music/score layback/editing and the mix. On large budget films there may be, as APE said, a very big audio post team; on low/no/mini/micro budget projects there are guys like me who do all the aspects of audio post plus the whole gamut of variations in between. As with the production sound the optimum choice is to hire a professional supervising sound editor/sound designer. Second best is an ambitious up-and-comer. The final choice is, of course, to do it all yourself. If you are going to DIY you could start with the following:
Dialog Editing - John Purcell
The Foley Grail - Vanessa Ament
The Sound Effects Bible - Ric Viers
Sound and Vision - Michael Chion
Sound Design - David Sonnenschein
Producing Great Sound for Film and Video - Jay Rose
Practical Art of Motion Picture Sound - David Lewis Yewdall
You may also want to spend a few days (or more) at filmsound.org; lots of basic definitions and sound-for-picture history as well as great articles by and about some phenomenal sound folks.
Audio post is a complex topic, and gearing up for production sound and audio post can be daunting, as well as (relatively) pricey, not to mention the skill sets that need to be acquired. Don't let this discourage you; you opened this particular (but very fascinating and rewarding) can of worms, which shows you care about the sound of your projects. GOOD FOR YOU!!!! All you have to remember is:
Your project will only look as good as it sounds, because
"Sound is half of the experience."
and you'll be fine.
Good Luck!!!!!!!