Well, I own my custom home building/full service remodeling company. So for my flips/rentals, I'm at "somewhat" a advantage over other who hires contractor. :)
But this is my experience:
For the longest time, I used to bid pretty low as a whole sale price for investors to remodel their flips. For the cheaper flips, it works out great. These are low end houses, or rentals/apartments etc..., where we would not care as much on quality but rather speed. Things like painting: we would spray the whole house with one color, one coat kinda thing - quick and dirty. Moldings (baseboard, door trims etc...) would just get one quick coat as well. Kitchen would be RTA (ready-to-assemble cabinets) with prefabricated granite counter top. 2 guys would be able to finish a 10x10 kitchen in 1 1/2 day. Shower wall is the full sheet (vs tiles, marble/natural stone which requires custom fabrication). Windows would be retrofit styles, 30 minutes a window to replace type of deal. etc... So we can come in and get out fairly quickly and still make a little profit.
But as the properties get higher in prices, hence the quality requirement, we have to charge "custom" prices for it. Now clients would want level 5 wall finish (smooth surface vs textured) which takes 3-4 times longer; paint would have to be super sharp on color transitions (1 coat primer, at least 2 top coats); all baseboard and trim work & paint have to be perfect: no brush mark, no visible nail holes etc; and all everything else in between.
So my point is: beside using your elbow grease to gain sweet equity, pricing is subjective to quality. :) You can get cheaper a little bit, but don't get the cheapest hacker you can find. Contractors like our company would come back and do touch up, fix minor leaks/defects etc... no matter no cheap/expensive the project is. Not the cheap hack. They'll be gone before you know. So contractor reputation, recommendations (like above posts suggested) and be fair to contractors in term of prices, are more important for long term. Interviewing at least 3-4 contractors to narrow down 1-2, then try them for a couple of projects for size. Then build a relationship for future projects.
Just my 2 cents.
