I want to point out a few things that I've learned over the years of doing this kind of stuff that appears to be lost in this conversation.
First, I haven't seen anything that is looking at your clients application specifics. Simply put, what specific applications is your client using, or what do they want to use, if this is a green-field?
Second, how will they be accessing those applications, are they client-server based, Web based, Remote Desktop, etc.?
Third, you really need to examine your support avenues. In my most recent experiences with the support organizations of HP and IBM, I really like IBM hardware by the way, I have found them lacking, unless I have signed my clients up for some very expensive support options. Everything on the lower tiers goes offshore. Dell, on the other hand, though I am not a fan of their hardware, have some decent support offerings, and are based in the US.
Fourth, are you reselling, implementing and supporting? Or some derivative?
Now, let's get into some basics, my philosophy is design from the OSI model, top down, Layer 7 to 1. Implement from the bottom up, Layer 1 to 7. Makes everything simpler and keeps your head in the right frame of reference. Also it ensures you know everything.
Does your $250k budget encompass infrastructure, network and computing, support? If so, your budget for hardware just got cut by 30%. How much does implementation cost? You need to factor that in. The customer has done you a real favor by defining the budget you need to work within.
All that being said, now, let's look at your hardware and software you have described.
SAN - you don't have enough money for a SAN. A SAN will triple the cost of the infrastructure to support it. A NAS is your best cost-performance option.
Blade servers - cost-performance is again, way out of line for your budget.
This is a small outfit currently, where are they going to scale to as far a number of workstations to support? SBS while its great for a very limited growth organization, you're too close to maxing out the capabilities. An forget about Linux and others. This is probably a primarily Microsoft environment, don't make your life difficult, stay with Microsoft software - 32 bit. Server 2003 R2 or some derivation, not many small Enterprise applications are supported under 64-bit software other than native 64 bit Microsoft apps.
Network switching - small Enterprise - Some of the HP ProCurve Web managed 24-port L2 switches should work well, low-cost, good quality and they have VLAN capabilities, if needed, as the organization needs to segment, if they need segmentation at all. If they want to do segmentation, you'll need a L3 switch at the core to route the VLANs. This can be implemented now, without having to turn on all the features or use the L3 capabilities. Find something with "throw-away" capabilities, and keep a spare switch, no sense is spending a great deal of money on network switch support contracts for an Enterprise this size.
Servers: Active Directory (authentication), Exchange for collaboration (will do email-Outlook, scheduling-Outlook and project management-Project), Storage, Database-MS SQL, CAD-? - total 5. No knowing what your specific applications are using these services for limits the amount of advice.... I would need to know the design goals for each of the servers to advise in any constructive manner.
Desktops - ditch Vista, WinXP Pro only. You don't need the Vista headaches.
Wireless - I would avoid unless your going to set up WPA2-Enterprise with Active Directory. If that's your plan, go with fat APs from Cisco, Proxim, etc. The wireless switches with thin APs are great for large deployments, a headache and expensive for 1-3 AP deployements.
Heat - how big and well ventilated is the server room/closet/etc. Have you thought about your cooling requirements? 5 servers are going to kick out a lot of heat, and they're only going to operate good up to about 95F. One watt consumed is equal to 3.412 Btu/hr. To calculate tons of air conditioning required, multiply the total wattage consumed by 0.000285 or as some AC units are measured in BTU, it should be 1-2x, BTU produced versus dissipated.
UPS - This is kinda like cooling requirements, it depends on what a normal load consumes. Stick with someone real, I typically use Liebert, Eaton (PowerWare, BEST) or General Electric. These guys usually have some very good environmental monitoring capabilities as well. You want to UPS to signal your servers through a network port... Hopefully your servers are equipped with out-of-band remote management capabilities, and this would be a perfect entry point. This is not a place for USB ports. And remember, if the AC power to the building fails, the air conditioning fails too. You want just enough run-time to allow for a 5 or 10-minute power outage and then a graceful shutdown of your servers.
Help me understand where you are wanting to go with all of this.