While the question has been asked and answered (and very well) ... being that I'm sort of an ol' timey networking sort, and feeling scrappy ... let me give you a different approach for your consideration.
1) Don't do a wide-scale wireless LAN in this scenario
2) Use a wired LAN for the fixed PCs, use wireless for conference rooms or other management gathering places (assumes managers have laptops), maybe some sort of Guest access that is partitioned from the common corporate network.
While current wireless (i.e., EAP / 802.1x -based) is much more secure than previous generations (i.e., WEP, MAC filters, etc), the physical security of a wired LAN is still generally better and easier to "defend" (you can put cabling in conduits / raceways, and terminte it behind closed & locked doors ).
Cabling is faster and more efficient, can more easily be upgraded to newer speeds (i.e., GigE, 10GigE) and is easier to partition the traffic (VLANs / broadcast domains)
I can go on for while, but I think you get the idea.
SO(!) make the following assumptions ("anything is valid if you support it with the proper assumptions"):
The person that WANTS (note: not "Needs")the wireless network doesn't understand any of the above ( and assciated problems) They want it because they think it's cool, neat, exciting technology (and it is, just not for "everywhere") .... and once you explain it to them, they will see the light and go cabled general network with wireless supporting specific functions (conferences, guests, consultants, etc)
Costs may be higher initially (predominantly labor), but the cabled network will likely have better "legs" and adapt better to future technological advances.
Even if / when wireless can handle the same traffic loads (wireless is a shared medium, like a hub) at the same speeds, chances are you'll need a cabled backbone architecture to connect all that wireless stuff you need to distribute around the office (still a valid part of the investment).
Use POE-capable switches, so future migration / expansion of the wireless infrastructure is supported (also IP Phones in addition to the POE-capable APs)
Service devices / web servers / hardware firewalls / network servers / addressing all remain the same for either wired or wireless (you'd have to be a raving idiot to put servers / shared resources on wireless without a *real* good reason).
Anyway, you get the idea. Break out of the box, don't take the "use wireless" bait ... tell 'em like it is, even though educators aren't likely to be well-grounded in reality.
The "Class C address" block is a ringer: The internal network would likely be / oughta be / don't be stupid an RFC1918 address block (10.x.x.x, 172.16-31.x.x, 192.168.0-255.x), with some smaller block of "Class C" public addresses reserved for inbound Web access (and maybe a couple for outbound PAT) defined on the external interface(s) of your firewall.
If you really have to come up with a Bill of Materials, don't forget things like UPS, racks, jumpers, *** AIR CONDITIONING FOR THE DATA CENTER (duh)*** and the **** CLOSETS*** that will have the access-level devices ...
A power audit and possible installation / upgrade for the data center and closets (how many closets have you seen with a couple 20A circuits? )...
Money for service contracts (maintenance, software updates for router / switch / ap / Call Manager, IP phones ... whatever)
And (this is a margin builder) routine "check up" visits (it keeps your face fresh so the customer won't forget you and you get to tell him of the new, neat, and exciting technology that he can't live without .. it's a "keep the salesman fed, and he will keep you fed" kind of program.
Like I said, there's more ... if you need more let us know. This is just my take on the information you've presented.
Good Luck
Scott
