I know id varies widely from market to market, but when compiling a project budget for an indy documentary, what are some reasonable figures to include for daily rates for director, camera op, sound op, and producer?

Is a flat fee an option for the director and/or producer?

i'm assuming you're looking at a director who is not in the guild.
If that's the case it's certainly reasonable to offer a flat rate, but I would be a little leary myself. With a day rate the person knows how much to expect and knows they are expected to work while on the clock.

FLat rates can get sketchy when the payee decides they put their fair share of work in for what they were getting paid.

With producers, I think it's not uncommon for them to work on a flat percentage of the budget.

For misc crew anything from $100/day for mildly experienced on up from there. And you can normally negotiate lower day rates if you promise multiple days. Many people offer 5 days at a 4 day rate or something like that.
I worked on a no-budget feature a few years back and we had several dp's and people with full grip trucks quoting us $75-100 a day. Yes, it's a crazy price, but if you're making payments on a grip truck that's just sitting out in your driveway...

the Doc's i know pay .... 1200-1500 for cameraperson ( including camera - for over time $$ is usually split - camera/labor ) , sound 450 with basic equipment- recorder ,boom mic , hard wire lav - wireless are added $ .. gaffers 450 -equipment extra .... all $$ based on 10hr days ...
Producers are usually on monthly salary flat rate for 6-18 months ( the ones i know get approx 1100-1500 week)