Well, Its complicated.Take http://www.hooyou.com/services/attorneyfee/index.html as example. I think their fees are reasonable.
Say, if you hire a lawyer the lowest cost to you will be $5525. If you have a wife you need to pay $385+$500+$150.
1. $3800 for I140 to lawyer
2. $190 I140 filing fee to USCIS
3. $1000 for I485 to lawyer.
4. $385 I485 filing fee to USCIS for each person
5. $150 for medical exam (The cheapest price) for each person.
My case is DIY. I paid $190 (I140) + 3x $385 (I485) + 3x$150 (medical exam) + $165 (AP) + $175 (EAD).
Also, I am a very conervative guy. Even I already have 140 approved, I still have my H-1B extended for another 3 years, it costed me $195+$185.
Good luck to everybody in this place