Delaware has a long, clear history of case law, which is why many companies are incorporated there. Alot are also incorporated in Nevada (my home state). There it's like 200$ total. For a start-up, you normally don't need a whole lot of "lawyer juice" in the equation. The forms are very simple. You basically fill out the articles of incorporation document, then fill out a listing of officers/board members (initial listing of officers), which can be changed later. You also need to have a resident agent, which doesn't need to be a physical place, so long as lawsuit stuff can get there. Many places offer resident agencies as a service for as little as 99$. The deputy just needs to be able to deliver you some lawsuit/whatever. You send it all off to the secretary of state in whatever state you wish to incorporate, then in a few weeks later you get a copy of the forms back plus a certificate signed by the secretary of state saying that you're incorporated under that state. Normally all states have a website where you can look up information about a particular corporation. Every year you have to pay a few hundred bucks or so to rewnew the initial listing of officers. It gets a little more complex if you have investors and the company is initially shared between several people/other companies, but overall, its really that simple.

Delaware might charge more because of the simple fact that so many companies incorporate there. Finally, those "incorporate" services that charge a few grand basically give little advice and just fill the paper work out for you. They take advantage of the naive.