If you decide to undertake the job yourselves, it will involve demo of the wall and temporary support, reframing the new opening, and Installing the new header. A big job, but very "do-able" if you take your time. I suggest you consult with an engineer (about 65 bucks per hour and an hour should be PLENTY of time) should you decide to DIY.
Don't give up on finding a reputable contractor. Ask around and let them know the experiences you've been encountering. Another option would be to consult with a structural engineer, and sub the work out yourselves as you go.