Gigabit can be saturated too. Don't just assume that it's fast enough.
In what sense? You're supposed to put in cables and switches and routers and whatnot without any real regard for how they are going to be used?
Huh? Building a network barring some unforseen circumstance is certainly feasible. This is not usually an issue. The issue is how to go about it.
In the US it's going to be on the order of ten times that. A good budgetary number for that part of the system would be around $150K, which includes a factor for lack of definition.
What kind of computers, what network interfaces do they have, what operating system are they running, what applications are installed, to what purpose are they used, what capability is the network expected to provide that is not already present?
You will. YOU _WILL_.
In whose control will it be? I am not at all clear on your role in this.
If you think that you're not going to be responsible, then put in another $25K or so for a _good_ lawyer to write up the contracts. Don't bother to warn users, you may as well attempt to raise sea level by peeing in the ocean.
Famous last words.
My view on this is that you are badly, horribly out of your depth. Hire someone who has built a network this size before to do the work and watch over his shoulder so you learn how it's done.
Using unmanaged switches on a network this size is out of the question. You are going to have no diagnostic capability at all, and with this many ports to deal with you _need_ the diagnostic capability. Whether routers will be useful depends on information that you have not provided concerning the manner in which the network will be used. In any case, compared to the operating costs the costs of using a router instead of a switch in a given location is negligible.
You need at least one and possibly several domain controllers. Any web server should be independent of the domain controllers. The DNS server will typically be on one of the domain controllers.
Uh, how were you going to run this _without_ a DNS server? Were you going to pay for 750 or so IP addresses from your service provider?
So you're going to run around setting IP addresses? Setting up DHCP is practically trivial, far, far simpler than setting static addresses on hundreds of computers.
WHY?
Huh? You're saying that your users just won't print? Do be sure to have an armored door on your office and under no circumstances let anyone know your home address.
The owner of the building is going to put in on the order of 800 CAT5E drops for enough under $10K that you can afford to buy switches etc with the change?
Ease of installation does not equal ease of management. If the building is too large to permit all wiring on a floor to be home-run to a single closet then you want to run it to as few as possible.
So how will they get done? Hint, if you don't put in servers for this then they're going to be bombing your Internet connection instead.
You think that do you? Telephone is not a substitute for email, email is not a substitute for telephone, they serve different purposes.
You need to have a real handle on the load--a "meaty" internet connection can cost thousands of dollars a month.
I think that you need to do some more planning. Like how are you going to install software on individual computers, are you going to go around at 2AM with a CD in your hand? And what keeps the user from removing it?
From the questions you are asking, the costs you are coming up with, and the assumptions you are making it is clear that you don't have a good understanding of the real issues in running a network this size. Relying on the skill and good will of the users is a recipe for failure.