Form my limited rehab experience, I find hiring a general contractor to do a job ends up being nearly double the cost of me hiring tradesmen directly. For example, if I need some framing, plumbing, cement work, and cabinets installed, I may get a $20k quote while if I hire these tradesmen directly and individually, it might cost me $12k total.
What you get by hiring a general contractor is a manager that is supposed to keep the project going and deliver quality work on time. This doesn't always happen and some general contractors save costs for themselves by hiring less than qualified specialists to do the work.
What you get by hiring tradesmen directly is the ability to select someone with a skill level you want to actually do the work. If yo choose poorly, you still get poor quality work. You also have to do more micromanagement with this approach. I have chosen this approach most often. I've found tradesmen can range from very good to unacceptable. This approach also takes longer to complete the job which means opportunity cost. So weigh both choices.
As far as actual cost goes, the baseline for good work is the going rate of a tradesman in the field you need. These rates vary depending on what the job is. Then there is the marked multiplier. In San Francisco electrical work may cost 4X more than the same work in Tucson for example. This is a market multiplier. Its the same work, takes the same skill, and the same materials. However in one market you have people with million dollar+ homes paying you and the other market you have people with $200K homes paying you. If the customers have more cash, rates are higher.
