Since most of the actual work is cloud computing, "cloud," I don't really see a need for a server, especially with only 4 users.
4 computers (depending on how strong you need them) can run about 500-1000 from, say Dell. It could be much cheaper from other manufacturers, but then again those prices usually include Office 2007. Since you are cloud computing, then that saves you about 200 per computer. Perhaps invest it into bigger LCD screens. Even those are very cheap nowadays. Optiplex machines are very scalable if you decide to upgrade later on and are reasonably priced.
Since you are a very small network 4 ppl, you could get a package deal with an ISP or phone company, like for example Verizon, check this out: http://smallbusiness.verizon.com/bundles/
You can save a ton bundling, Internet, Voice/Cell into one bill. You won't be using a T1 internet connection in these bundles but with 4 people, I think you guys can get away with a good fiber optic or DSL connection, they are extremely fast for a fraction of the price. (30-80$ without a package)
Help Desk support is going to cost you depending if its a contractor, or an outsourced company, I'd compare, you most likely though won't need them a lot after it's fine tuned. You may get a better price from someone looking for clients than a company dedicated to support. But then quality may suffer, but then again, it's not like you can't fire them for bad work. For example if you just hire someone to fix a problem, expect a person to charge you anywhere from 30 to 75$ an hour, not including hardware that is replaced, driving fee (if any) etc. I personally never did a support job for anything less than 35$/hr, but that's me, others may charge less, others much more, so call around.
A good HP Laser jet printer probably around 500~ depending where you go. You want a workhorse, especially for accounting reports. But then it all depends if you need color and what size paper you need.
The only networking equipment you really need is a switch, to share data with eachother. A good NetGear 8-12 port switch should cost you about 20-30$. Don't forget you'll need CAT5/6 cables which are usually cheap you if make them yourself. Or you could go wireless, but then you'd have to worry about security, encryption, wireless card devices for each computer etc.
While you could create a simply network with shares on each workstation, you could also invest in a small network area storage server, such as SNAP servers ranging in about 200-500$ depending on size and features. Or you could simply purchase an extra computer and put all your data there, but remember, standard Windows OSes do not allow more than 10 connections, so if you grow you'll be stuck. Though Windows 7 Ultimate allows 20 I believe (more if you hack it.)
An on going cost is going to be power from 4 computers, monitors, and a printer, toner and paper. Additionally, you may want to look into buying BATTERY BACKUPs from APC, perhaps the APC SMART UPS RS 800s for quality and good battery time. If you want cheaper, just get their much smaller versions, but with less battery time. You'd hate the power to go out during some accounting transactions.
Hopefully that gives you an idea possible solutions. For the most part you have everything covered except the UPSs I mentioned and perhaps a file sharing device.